text: /* Copyright (C) 2010-2020 The RetroArch team
   *
   * ---------------------------------------------------------------------------------------
   * The following license statement only applies to this libretro API header (libretro.h).
   * ---------------------------------------------------------------------------------------
   *
   * Permission is hereby granted, free of charge,
   * to any person obtaining a copy of this software and associated documentation files (the "Software"),
   * to deal in the Software without restriction, including without limitation the rights to
   * use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software,
   * and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
   *
   * The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
   *
   * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED,
   * INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
   * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
   * IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
   * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
   * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
   */
  
  #ifndef LIBRETRO_H__
  #define LIBRETRO_H__
  
  #include <stdint.h>
  #include <stddef.h>
  #include <limits.h>
  
  #ifdef __cplusplus
  extern "C" {
  #endif
  
  #ifndef __cplusplus
  #if defined(_MSC_VER) && _MSC_VER < 1800 && !defined(SN_TARGET_PS3)
  /* Hack applied for MSVC when compiling in C89 mode
   * as it isn't C99-compliant. */
  #define bool unsigned char
  #define true 1
  #define false 0
  #else
  #include <stdbool.h>
  #endif
  #endif
  
  #ifndef RETRO_CALLCONV
  #  if defined(__GNUC__) && defined(__i386__) && !defined(__x86_64__)
  #    define RETRO_CALLCONV __attribute__((cdecl))
  #  elif defined(_MSC_VER) && defined(_M_X86) && !defined(_M_X64)
  #    define RETRO_CALLCONV __cdecl
  #  else
  #    define RETRO_CALLCONV /* all other platforms only have one calling convention each */
  #  endif
  #endif
  
  #ifndef RETRO_API
  #  if defined(_WIN32) || defined(__CYGWIN__) || defined(__MINGW32__)
  #    ifdef RETRO_IMPORT_SYMBOLS
  #      ifdef __GNUC__
  #        define RETRO_API RETRO_CALLCONV __attribute__((__dllimport__))
  #      else
  #        define RETRO_API RETRO_CALLCONV __declspec(dllimport)
  #      endif
  #    else
  #      ifdef __GNUC__
  #        define RETRO_API RETRO_CALLCONV __attribute__((__dllexport__))
  #      else
  #        define RETRO_API RETRO_CALLCONV __declspec(dllexport)
  #      endif
  #    endif
  #  else
  #      if defined(__GNUC__) && __GNUC__ >= 4 && !defined(__CELLOS_LV2__)
  #        define RETRO_API RETRO_CALLCONV __attribute__((__visibility__("default")))
  #      else
  #        define RETRO_API RETRO_CALLCONV
  #      endif
  #  endif
  #endif
  
  /* Used for checking API/ABI mismatches that can break libretro
   * implementations.
   * It is not incremented for compatible changes to the API.
   */
  #define RETRO_API_VERSION         1
  
  /*
   * Libretro's fundamental device abstractions.
   *
   * Libretro's input system consists of some standardized device types,
   * such as a joypad (with/without analog), mouse, keyboard, lightgun
   * and a pointer.
   *
   * The functionality of these devices are fixed, and individual cores
   * map their own concept of a controller to libretro's abstractions.
   * This makes it possible for frontends to map the abstract types to a
   * real input device, and not having to worry about binding input
   * correctly to arbitrary controller layouts.
   */
  
  #define RETRO_DEVICE_TYPE_SHIFT         8
  #define RETRO_DEVICE_MASK               ((1 << RETRO_DEVICE_TYPE_SHIFT) - 1)
  #define RETRO_DEVICE_SUBCLASS(base, id) (((id + 1) << RETRO_DEVICE_TYPE_SHIFT) | base)
  
  /* Input disabled. */
  #define RETRO_DEVICE_NONE         0
  
  /* The JOYPAD is called RetroPad. It is essentially a Super Nintendo
   * controller, but with additional L2/R2/L3/R3 buttons, similar to a
   * PS1 DualShock. */
  #define RETRO_DEVICE_JOYPAD       1
  
  /* The mouse is a simple mouse, similar to Super Nintendo's mouse.
   * X and Y coordinates are reported relatively to last poll (poll callback).
   * It is up to the libretro implementation to keep track of where the mouse
   * pointer is supposed to be on the screen.
   * The frontend must make sure not to interfere with its own hardware
   * mouse pointer.
   */
  #define RETRO_DEVICE_MOUSE        2
  
  /* KEYBOARD device lets one poll for raw key pressed.
   * It is poll based, so input callback will return with the current
   * pressed state.
   * For event/text based keyboard input, see
   * RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK.
   */
  #define RETRO_DEVICE_KEYBOARD     3
  
  /* LIGHTGUN device is similar to Guncon-2 for PlayStation 2.
   * It reports X/Y coordinates in screen space (similar to the pointer)
   * in the range [-0x8000, 0x7fff] in both axes, with zero being center and
   * -0x8000 being out of bounds.
   * As well as reporting on/off screen state. It features a trigger,
   * start/select buttons, auxiliary action buttons and a
   * directional pad. A forced off-screen shot can be requested for
   * auto-reloading function in some games.
   */
  #define RETRO_DEVICE_LIGHTGUN     4
  
  /* The ANALOG device is an extension to JOYPAD (RetroPad).
   * Similar to DualShock2 it adds two analog sticks and all buttons can
   * be analog. This is treated as a separate device type as it returns
   * axis values in the full analog range of [-0x7fff, 0x7fff],
   * although some devices may return -0x8000.
   * Positive X axis is right. Positive Y axis is down.
   * Buttons are returned in the range [0, 0x7fff].
   * Only use ANALOG type when polling for analog values.
   */
  #define RETRO_DEVICE_ANALOG       5
  
  /* Abstracts the concept of a pointing mechanism, e.g. touch.
   * This allows libretro to query in absolute coordinates where on the
   * screen a mouse (or something similar) is being placed.
   * For a touch centric device, coordinates reported are the coordinates
   * of the press.
   *
   * Coordinates in X and Y are reported as:
   * [-0x7fff, 0x7fff]: -0x7fff corresponds to the far left/top of the screen,
   * and 0x7fff corresponds to the far right/bottom of the screen.
   * The "screen" is here defined as area that is passed to the frontend and
   * later displayed on the monitor.
   *
   * The frontend is free to scale/resize this screen as it sees fit, however,
   * (X, Y) = (-0x7fff, -0x7fff) will correspond to the top-left pixel of the
   * game image, etc.
   *
   * To check if the pointer coordinates are valid (e.g. a touch display
   * actually being touched), PRESSED returns 1 or 0.
   *
   * If using a mouse on a desktop, PRESSED will usually correspond to the
   * left mouse button, but this is a frontend decision.
   * PRESSED will only return 1 if the pointer is inside the game screen.
   *
   * For multi-touch, the index variable can be used to successively query
   * more presses.
   * If index = 0 returns true for _PRESSED, coordinates can be extracted
   * with _X, _Y for index = 0. One can then query _PRESSED, _X, _Y with
   * index = 1, and so on.
   * Eventually _PRESSED will return false for an index. No further presses
   * are registered at this point. */
  #define RETRO_DEVICE_POINTER      6
  
  /* Buttons for the RetroPad (JOYPAD).
   * The placement of these is equivalent to placements on the
   * Super Nintendo controller.
   * L2/R2/L3/R3 buttons correspond to the PS1 DualShock.
   * Also used as id values for RETRO_DEVICE_INDEX_ANALOG_BUTTON */
  #define RETRO_DEVICE_ID_JOYPAD_B        0
  #define RETRO_DEVICE_ID_JOYPAD_Y        1
  #define RETRO_DEVICE_ID_JOYPAD_SELECT   2
  #define RETRO_DEVICE_ID_JOYPAD_START    3
  #define RETRO_DEVICE_ID_JOYPAD_UP       4
  #define RETRO_DEVICE_ID_JOYPAD_DOWN     5
  #define RETRO_DEVICE_ID_JOYPAD_LEFT     6
  #define RETRO_DEVICE_ID_JOYPAD_RIGHT    7
  #define RETRO_DEVICE_ID_JOYPAD_A        8
  #define RETRO_DEVICE_ID_JOYPAD_X        9
  #define RETRO_DEVICE_ID_JOYPAD_L       10
  #define RETRO_DEVICE_ID_JOYPAD_R       11
  #define RETRO_DEVICE_ID_JOYPAD_L2      12
  #define RETRO_DEVICE_ID_JOYPAD_R2      13
  #define RETRO_DEVICE_ID_JOYPAD_L3      14
  #define RETRO_DEVICE_ID_JOYPAD_R3      15
  
  #define RETRO_DEVICE_ID_JOYPAD_MASK    256
  
  /* Index / Id values for ANALOG device. */
  #define RETRO_DEVICE_INDEX_ANALOG_LEFT       0
  #define RETRO_DEVICE_INDEX_ANALOG_RIGHT      1
  #define RETRO_DEVICE_INDEX_ANALOG_BUTTON     2
  #define RETRO_DEVICE_ID_ANALOG_X             0
  #define RETRO_DEVICE_ID_ANALOG_Y             1
  
  /* Id values for MOUSE. */
  #define RETRO_DEVICE_ID_MOUSE_X                0
  #define RETRO_DEVICE_ID_MOUSE_Y                1
  #define RETRO_DEVICE_ID_MOUSE_LEFT             2
  #define RETRO_DEVICE_ID_MOUSE_RIGHT            3
  #define RETRO_DEVICE_ID_MOUSE_WHEELUP          4
  #define RETRO_DEVICE_ID_MOUSE_WHEELDOWN        5
  #define RETRO_DEVICE_ID_MOUSE_MIDDLE           6
  #define RETRO_DEVICE_ID_MOUSE_HORIZ_WHEELUP    7
  #define RETRO_DEVICE_ID_MOUSE_HORIZ_WHEELDOWN  8
  #define RETRO_DEVICE_ID_MOUSE_BUTTON_4         9
  #define RETRO_DEVICE_ID_MOUSE_BUTTON_5         10
  
  /* Id values for LIGHTGUN. */
  #define RETRO_DEVICE_ID_LIGHTGUN_SCREEN_X        13 /*Absolute Position*/
  #define RETRO_DEVICE_ID_LIGHTGUN_SCREEN_Y        14 /*Absolute*/
  #define RETRO_DEVICE_ID_LIGHTGUN_IS_OFFSCREEN    15 /*Status Check*/
  #define RETRO_DEVICE_ID_LIGHTGUN_TRIGGER          2
  #define RETRO_DEVICE_ID_LIGHTGUN_RELOAD          16 /*Forced off-screen shot*/
  #define RETRO_DEVICE_ID_LIGHTGUN_AUX_A            3
  #define RETRO_DEVICE_ID_LIGHTGUN_AUX_B            4
  #define RETRO_DEVICE_ID_LIGHTGUN_START            6
  #define RETRO_DEVICE_ID_LIGHTGUN_SELECT           7
  #define RETRO_DEVICE_ID_LIGHTGUN_AUX_C            8
  #define RETRO_DEVICE_ID_LIGHTGUN_DPAD_UP          9
  #define RETRO_DEVICE_ID_LIGHTGUN_DPAD_DOWN       10
  #define RETRO_DEVICE_ID_LIGHTGUN_DPAD_LEFT       11
  #define RETRO_DEVICE_ID_LIGHTGUN_DPAD_RIGHT      12
  /* deprecated */
  #define RETRO_DEVICE_ID_LIGHTGUN_X                0 /*Relative Position*/
  #define RETRO_DEVICE_ID_LIGHTGUN_Y                1 /*Relative*/
  #define RETRO_DEVICE_ID_LIGHTGUN_CURSOR           3 /*Use Aux:A*/
  #define RETRO_DEVICE_ID_LIGHTGUN_TURBO            4 /*Use Aux:B*/
  #define RETRO_DEVICE_ID_LIGHTGUN_PAUSE            5 /*Use Start*/
  
  /* Id values for POINTER. */
  #define RETRO_DEVICE_ID_POINTER_X         0
  #define RETRO_DEVICE_ID_POINTER_Y         1
  #define RETRO_DEVICE_ID_POINTER_PRESSED   2
  #define RETRO_DEVICE_ID_POINTER_COUNT     3
  
  /* Returned from retro_get_region(). */
  #define RETRO_REGION_NTSC  0
  #define RETRO_REGION_PAL   1
  
  /* Id values for LANGUAGE */
  enum retro_language
  {
     RETRO_LANGUAGE_ENGLISH             = 0,
     RETRO_LANGUAGE_JAPANESE            = 1,
     RETRO_LANGUAGE_FRENCH              = 2,
     RETRO_LANGUAGE_SPANISH             = 3,
     RETRO_LANGUAGE_GERMAN              = 4,
     RETRO_LANGUAGE_ITALIAN             = 5,
     RETRO_LANGUAGE_DUTCH               = 6,
     RETRO_LANGUAGE_PORTUGUESE_BRAZIL   = 7,
     RETRO_LANGUAGE_PORTUGUESE_PORTUGAL = 8,
     RETRO_LANGUAGE_RUSSIAN             = 9,
     RETRO_LANGUAGE_KOREAN              = 10,
     RETRO_LANGUAGE_CHINESE_TRADITIONAL = 11,
     RETRO_LANGUAGE_CHINESE_SIMPLIFIED  = 12,
     RETRO_LANGUAGE_ESPERANTO           = 13,
     RETRO_LANGUAGE_POLISH              = 14,
     RETRO_LANGUAGE_VIETNAMESE          = 15,
     RETRO_LANGUAGE_ARABIC              = 16,
     RETRO_LANGUAGE_GREEK               = 17,
     RETRO_LANGUAGE_TURKISH             = 18,
     RETRO_LANGUAGE_SLOVAK              = 19,
     RETRO_LANGUAGE_PERSIAN             = 20,
     RETRO_LANGUAGE_HEBREW              = 21,
     RETRO_LANGUAGE_ASTURIAN            = 22,
     RETRO_LANGUAGE_FINNISH             = 23,
     RETRO_LANGUAGE_INDONESIAN          = 24,
     RETRO_LANGUAGE_SWEDISH             = 25,
     RETRO_LANGUAGE_UKRAINIAN           = 26,
     RETRO_LANGUAGE_LAST,
  
     /* Ensure sizeof(enum) == sizeof(int) */
     RETRO_LANGUAGE_DUMMY          = INT_MAX
  };
  
  /* Passed to retro_get_memory_data/size().
   * If the memory type doesn't apply to the
   * implementation NULL/0 can be returned.
   */
  #define RETRO_MEMORY_MASK        0xff
  
  /* Regular save RAM. This RAM is usually found on a game cartridge,
   * backed up by a battery.
   * If save game data is too complex for a single memory buffer,
   * the SAVE_DIRECTORY (preferably) or SYSTEM_DIRECTORY environment
   * callback can be used. */
  #define RETRO_MEMORY_SAVE_RAM    0
  
  /* Some games have a built-in clock to keep track of time.
   * This memory is usually just a couple of bytes to keep track of time.
   */
  #define RETRO_MEMORY_RTC         1
  
  /* System ram lets a frontend peek into a game systems main RAM. */
  #define RETRO_MEMORY_SYSTEM_RAM  2
  
  /* Video ram lets a frontend peek into a game systems video RAM (VRAM). */
  #define RETRO_MEMORY_VIDEO_RAM   3
  
  /* Keysyms used for ID in input state callback when polling RETRO_KEYBOARD. */
  enum retro_key
  {
     RETROK_UNKNOWN        = 0,
     RETROK_FIRST          = 0,
     RETROK_BACKSPACE      = 8,
     RETROK_TAB            = 9,
     RETROK_CLEAR          = 12,
     RETROK_RETURN         = 13,
     RETROK_PAUSE          = 19,
     RETROK_ESCAPE         = 27,
     RETROK_SPACE          = 32,
     RETROK_EXCLAIM        = 33,
     RETROK_QUOTEDBL       = 34,
     RETROK_HASH           = 35,
     RETROK_DOLLAR         = 36,
     RETROK_AMPERSAND      = 38,
     RETROK_QUOTE          = 39,
     RETROK_LEFTPAREN      = 40,
     RETROK_RIGHTPAREN     = 41,
     RETROK_ASTERISK       = 42,
     RETROK_PLUS           = 43,
     RETROK_COMMA          = 44,
     RETROK_MINUS          = 45,
     RETROK_PERIOD         = 46,
     RETROK_SLASH          = 47,
     RETROK_0              = 48,
     RETROK_1              = 49,
     RETROK_2              = 50,
     RETROK_3              = 51,
     RETROK_4              = 52,
     RETROK_5              = 53,
     RETROK_6              = 54,
     RETROK_7              = 55,
     RETROK_8              = 56,
     RETROK_9              = 57,
     RETROK_COLON          = 58,
     RETROK_SEMICOLON      = 59,
     RETROK_LESS           = 60,
     RETROK_EQUALS         = 61,
     RETROK_GREATER        = 62,
     RETROK_QUESTION       = 63,
     RETROK_AT             = 64,
     RETROK_LEFTBRACKET    = 91,
     RETROK_BACKSLASH      = 92,
     RETROK_RIGHTBRACKET   = 93,
     RETROK_CARET          = 94,
     RETROK_UNDERSCORE     = 95,
     RETROK_BACKQUOTE      = 96,
     RETROK_a              = 97,
     RETROK_b              = 98,
     RETROK_c              = 99,
     RETROK_d              = 100,
     RETROK_e              = 101,
     RETROK_f              = 102,
     RETROK_g              = 103,
     RETROK_h              = 104,
     RETROK_i              = 105,
     RETROK_j              = 106,
     RETROK_k              = 107,
     RETROK_l              = 108,
     RETROK_m              = 109,
     RETROK_n              = 110,
     RETROK_o              = 111,
     RETROK_p              = 112,
     RETROK_q              = 113,
     RETROK_r              = 114,
     RETROK_s              = 115,
     RETROK_t              = 116,
     RETROK_u              = 117,
     RETROK_v              = 118,
     RETROK_w              = 119,
     RETROK_x              = 120,
     RETROK_y              = 121,
     RETROK_z              = 122,
     RETROK_LEFTBRACE      = 123,
     RETROK_BAR            = 124,
     RETROK_RIGHTBRACE     = 125,
     RETROK_TILDE          = 126,
     RETROK_DELETE         = 127,
  
     RETROK_KP0            = 256,
     RETROK_KP1            = 257,
     RETROK_KP2            = 258,
     RETROK_KP3            = 259,
     RETROK_KP4            = 260,
     RETROK_KP5            = 261,
     RETROK_KP6            = 262,
     RETROK_KP7            = 263,
     RETROK_KP8            = 264,
     RETROK_KP9            = 265,
     RETROK_KP_PERIOD      = 266,
     RETROK_KP_DIVIDE      = 267,
     RETROK_KP_MULTIPLY    = 268,
     RETROK_KP_MINUS       = 269,
     RETROK_KP_PLUS        = 270,
     RETROK_KP_ENTER       = 271,
     RETROK_KP_EQUALS      = 272,
  
     RETROK_UP             = 273,
     RETROK_DOWN           = 274,
     RETROK_RIGHT          = 275,
     RETROK_LEFT           = 276,
     RETROK_INSERT         = 277,
     RETROK_HOME           = 278,
     RETROK_END            = 279,
     RETROK_PAGEUP         = 280,
     RETROK_PAGEDOWN       = 281,
  
     RETROK_F1             = 282,
     RETROK_F2             = 283,
     RETROK_F3             = 284,
     RETROK_F4             = 285,
     RETROK_F5             = 286,
     RETROK_F6             = 287,
     RETROK_F7             = 288,
     RETROK_F8             = 289,
     RETROK_F9             = 290,
     RETROK_F10            = 291,
     RETROK_F11            = 292,
     RETROK_F12            = 293,
     RETROK_F13            = 294,
     RETROK_F14            = 295,
     RETROK_F15            = 296,
  
     RETROK_NUMLOCK        = 300,
     RETROK_CAPSLOCK       = 301,
     RETROK_SCROLLOCK      = 302,
     RETROK_RSHIFT         = 303,
     RETROK_LSHIFT         = 304,
     RETROK_RCTRL          = 305,
     RETROK_LCTRL          = 306,
     RETROK_RALT           = 307,
     RETROK_LALT           = 308,
     RETROK_RMETA          = 309,
     RETROK_LMETA          = 310,
     RETROK_LSUPER         = 311,
     RETROK_RSUPER         = 312,
     RETROK_MODE           = 313,
     RETROK_COMPOSE        = 314,
  
     RETROK_HELP           = 315,
     RETROK_PRINT          = 316,
     RETROK_SYSREQ         = 317,
     RETROK_BREAK          = 318,
     RETROK_MENU           = 319,
     RETROK_POWER          = 320,
     RETROK_EURO           = 321,
     RETROK_UNDO           = 322,
     RETROK_OEM_102        = 323,
  
     RETROK_LAST,
  
     RETROK_DUMMY          = INT_MAX /* Ensure sizeof(enum) == sizeof(int) */
  };
  
  enum retro_mod
  {
     RETROKMOD_NONE       = 0x0000,
  
     RETROKMOD_SHIFT      = 0x01,
     RETROKMOD_CTRL       = 0x02,
     RETROKMOD_ALT        = 0x04,
     RETROKMOD_META       = 0x08,
  
     RETROKMOD_NUMLOCK    = 0x10,
     RETROKMOD_CAPSLOCK   = 0x20,
     RETROKMOD_SCROLLOCK  = 0x40,
  
     RETROKMOD_DUMMY = INT_MAX /* Ensure sizeof(enum) == sizeof(int) */
  };
  
  /* If set, this call is not part of the public libretro API yet. It can
   * change or be removed at any time. */
  #define RETRO_ENVIRONMENT_EXPERIMENTAL 0x10000
  /* Environment callback to be used internally in frontend. */
  #define RETRO_ENVIRONMENT_PRIVATE 0x20000
  
  /* Environment commands. */
  #define RETRO_ENVIRONMENT_SET_ROTATION  1  /* const unsigned * --
                                              * Sets screen rotation of graphics.
                                              * Valid values are 0, 1, 2, 3, which rotates screen by 0, 90, 180,
                                              * 270 degrees counter-clockwise respectively.
                                              */
  #define RETRO_ENVIRONMENT_GET_OVERSCAN  2  /* bool * --
                                              * NOTE: As of 2019 this callback is considered deprecated in favor of
                                              * using core options to manage overscan in a more nuanced, core-specific way.
                                              *
                                              * Boolean value whether or not the implementation should use overscan,
                                              * or crop away overscan.
                                              */
  #define RETRO_ENVIRONMENT_GET_CAN_DUPE  3  /* bool * --
                                              * Boolean value whether or not frontend supports frame duping,
                                              * passing NULL to video frame callback.
                                              */
  
                                             /* Environ 4, 5 are no longer supported (GET_VARIABLE / SET_VARIABLES),
                                              * and reserved to avoid possible ABI clash.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_MESSAGE   6  /* const struct retro_message * --
                                              * Sets a message to be displayed in implementation-specific manner
                                              * for a certain amount of 'frames'.
                                              * Should not be used for trivial messages, which should simply be
                                              * logged via RETRO_ENVIRONMENT_GET_LOG_INTERFACE (or as a
                                              * fallback, stderr).
                                              */
  #define RETRO_ENVIRONMENT_SHUTDOWN      7  /* N/A (NULL) --
                                              * Requests the frontend to shutdown.
                                              * Should only be used if game has a specific
                                              * way to shutdown the game from a menu item or similar.
                                              */
  #define RETRO_ENVIRONMENT_SET_PERFORMANCE_LEVEL 8
                                             /* const unsigned * --
                                              * Gives a hint to the frontend how demanding this implementation
                                              * is on a system. E.g. reporting a level of 2 means
                                              * this implementation should run decently on all frontends
                                              * of level 2 and up.
                                              *
                                              * It can be used by the frontend to potentially warn
                                              * about too demanding implementations.
                                              *
                                              * The levels are "floating".
                                              *
                                              * This function can be called on a per-game basis,
                                              * as certain games an implementation can play might be
                                              * particularly demanding.
                                              * If called, it should be called in retro_load_game().
                                              */
  #define RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY 9
                                             /* const char ** --
                                              * Returns the "system" directory of the frontend.
                                              * This directory can be used to store system specific
                                              * content such as BIOSes, configuration data, etc.
                                              * The returned value can be NULL.
                                              * If so, no such directory is defined,
                                              * and it's up to the implementation to find a suitable directory.
                                              *
                                              * NOTE: Some cores used this folder also for "save" data such as
                                              * memory cards, etc, for lack of a better place to put it.
                                              * This is now discouraged, and if possible, cores should try to
                                              * use the new GET_SAVE_DIRECTORY.
                                              */
  #define RETRO_ENVIRONMENT_SET_PIXEL_FORMAT 10
                                             /* const enum retro_pixel_format * --
                                              * Sets the internal pixel format used by the implementation.
                                              * The default pixel format is RETRO_PIXEL_FORMAT_0RGB1555.
                                              * This pixel format however, is deprecated (see enum retro_pixel_format).
                                              * If the call returns false, the frontend does not support this pixel
                                              * format.
                                              *
                                              * This function should be called inside retro_load_game() or
                                              * retro_get_system_av_info().
                                              */
  #define RETRO_ENVIRONMENT_SET_INPUT_DESCRIPTORS 11
                                             /* const struct retro_input_descriptor * --
                                              * Sets an array of retro_input_descriptors.
                                              * It is up to the frontend to present this in a usable way.
                                              * The array is terminated by retro_input_descriptor::description
                                              * being set to NULL.
                                              * This function can be called at any time, but it is recommended
                                              * to call it as early as possible.
                                              */
  #define RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK 12
                                             /* const struct retro_keyboard_callback * --
                                              * Sets a callback function used to notify core about keyboard events.
                                              */
  #define RETRO_ENVIRONMENT_SET_DISK_CONTROL_INTERFACE 13
                                             /* const struct retro_disk_control_callback * --
                                              * Sets an interface which frontend can use to eject and insert
                                              * disk images.
                                              * This is used for games which consist of multiple images and
                                              * must be manually swapped out by the user (e.g. PSX).
                                              */
  #define RETRO_ENVIRONMENT_SET_HW_RENDER 14
                                             /* struct retro_hw_render_callback * --
                                              * Sets an interface to let a libretro core render with
                                              * hardware acceleration.
                                              * Should be called in retro_load_game().
                                              * If successful, libretro cores will be able to render to a
                                              * frontend-provided framebuffer.
                                              * The size of this framebuffer will be at least as large as
                                              * max_width/max_height provided in get_av_info().
                                              * If HW rendering is used, pass only RETRO_HW_FRAME_BUFFER_VALID or
                                              * NULL to retro_video_refresh_t.
                                              */
  #define RETRO_ENVIRONMENT_GET_VARIABLE 15
                                             /* struct retro_variable * --
                                              * Interface to acquire user-defined information from environment
                                              * that cannot feasibly be supported in a multi-system way.
                                              * 'key' should be set to a key which has already been set by
                                              * SET_VARIABLES.
                                              * 'data' will be set to a value or NULL.
                                              */
  #define RETRO_ENVIRONMENT_SET_VARIABLES 16
                                             /* const struct retro_variable * --
                                              * Allows an implementation to signal the environment
                                              * which variables it might want to check for later using
                                              * GET_VARIABLE.
                                              * This allows the frontend to present these variables to
                                              * a user dynamically.
                                              * This should be called the first time as early as
                                              * possible (ideally in retro_set_environment).
                                              * Afterward it may be called again for the core to communicate
                                              * updated options to the frontend, but the number of core
                                              * options must not change from the number in the initial call.
                                              *
                                              * 'data' points to an array of retro_variable structs
                                              * terminated by a { NULL, NULL } element.
                                              * retro_variable::key should be namespaced to not collide
                                              * with other implementations' keys. E.g. A core called
                                              * 'foo' should use keys named as 'foo_option'.
                                              * retro_variable::value should contain a human readable
                                              * description of the key as well as a '|' delimited list
                                              * of expected values.
                                              *
                                              * The number of possible options should be very limited,
                                              * i.e. it should be feasible to cycle through options
                                              * without a keyboard.
                                              *
                                              * First entry should be treated as a default.
                                              *
                                              * Example entry:
                                              * { "foo_option", "Speed hack coprocessor X; false|true" }
                                              *
                                              * Text before first ';' is description. This ';' must be
                                              * followed by a space, and followed by a list of possible
                                              * values split up with '|'.
                                              *
                                              * Only strings are operated on. The possible values will
                                              * generally be displayed and stored as-is by the frontend.
                                              */
  #define RETRO_ENVIRONMENT_GET_VARIABLE_UPDATE 17
                                             /* bool * --
                                              * Result is set to true if some variables are updated by
                                              * frontend since last call to RETRO_ENVIRONMENT_GET_VARIABLE.
                                              * Variables should be queried with GET_VARIABLE.
                                              */
  #define RETRO_ENVIRONMENT_SET_SUPPORT_NO_GAME 18
                                             /* const bool * --
                                              * If true, the libretro implementation supports calls to
                                              * retro_load_game() with NULL as argument.
                                              * Used by cores which can run without particular game data.
                                              * This should be called within retro_set_environment() only.
                                              */
  #define RETRO_ENVIRONMENT_GET_LIBRETRO_PATH 19
                                             /* const char ** --
                                              * Retrieves the absolute path from where this libretro
                                              * implementation was loaded.
                                              * NULL is returned if the libretro was loaded statically
                                              * (i.e. linked statically to frontend), or if the path cannot be
                                              * determined.
                                              * Mostly useful in cooperation with SET_SUPPORT_NO_GAME as assets can
                                              * be loaded without ugly hacks.
                                              */
  
                                             /* Environment 20 was an obsolete version of SET_AUDIO_CALLBACK.
                                              * It was not used by any known core at the time,
                                              * and was removed from the API. */
  #define RETRO_ENVIRONMENT_SET_FRAME_TIME_CALLBACK 21
                                             /* const struct retro_frame_time_callback * --
                                              * Lets the core know how much time has passed since last
                                              * invocation of retro_run().
                                              * The frontend can tamper with the timing to fake fast-forward,
                                              * slow-motion, frame stepping, etc.
                                              * In this case the delta time will use the reference value
                                              * in frame_time_callback..
                                              */
  #define RETRO_ENVIRONMENT_SET_AUDIO_CALLBACK 22
                                             /* const struct retro_audio_callback * --
                                              * Sets an interface which is used to notify a libretro core about audio
                                              * being available for writing.
                                              * The callback can be called from any thread, so a core using this must
                                              * have a thread safe audio implementation.
                                              * It is intended for games where audio and video are completely
                                              * asynchronous and audio can be generated on the fly.
                                              * This interface is not recommended for use with emulators which have
                                              * highly synchronous audio.
                                              *
                                              * The callback only notifies about writability; the libretro core still
                                              * has to call the normal audio callbacks
                                              * to write audio. The audio callbacks must be called from within the
                                              * notification callback.
                                              * The amount of audio data to write is up to the implementation.
                                              * Generally, the audio callback will be called continously in a loop.
                                              *
                                              * Due to thread safety guarantees and lack of sync between audio and
                                              * video, a frontend  can selectively disallow this interface based on
                                              * internal configuration. A core using this interface must also
                                              * implement the "normal" audio interface.
                                              *
                                              * A libretro core using SET_AUDIO_CALLBACK should also make use of
                                              * SET_FRAME_TIME_CALLBACK.
                                              */
  #define RETRO_ENVIRONMENT_GET_RUMBLE_INTERFACE 23
                                             /* struct retro_rumble_interface * --
                                              * Gets an interface which is used by a libretro core to set
                                              * state of rumble motors in controllers.
                                              * A strong and weak motor is supported, and they can be
                                              * controlled indepedently.
                                              * Should be called from either retro_init() or retro_load_game().
                                              * Should not be called from retro_set_environment().
                                              * Returns false if rumble functionality is unavailable.
                                              */
  #define RETRO_ENVIRONMENT_GET_INPUT_DEVICE_CAPABILITIES 24
                                             /* uint64_t * --
                                              * Gets a bitmask telling which device type are expected to be
                                              * handled properly in a call to retro_input_state_t.
                                              * Devices which are not handled or recognized always return
                                              * 0 in retro_input_state_t.
                                              * Example bitmask: caps = (1 << RETRO_DEVICE_JOYPAD) | (1 << RETRO_DEVICE_ANALOG).
                                              * Should only be called in retro_run().
                                              */
  #define RETRO_ENVIRONMENT_GET_SENSOR_INTERFACE (25 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_sensor_interface * --
                                              * Gets access to the sensor interface.
                                              * The purpose of this interface is to allow
                                              * setting state related to sensors such as polling rate,
                                              * enabling/disable it entirely, etc.
                                              * Reading sensor state is done via the normal
                                              * input_state_callback API.
                                              */
  #define RETRO_ENVIRONMENT_GET_CAMERA_INTERFACE (26 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_camera_callback * --
                                              * Gets an interface to a video camera driver.
                                              * A libretro core can use this interface to get access to a
                                              * video camera.
                                              * New video frames are delivered in a callback in same
                                              * thread as retro_run().
                                              *
                                              * GET_CAMERA_INTERFACE should be called in retro_load_game().
                                              *
                                              * Depending on the camera implementation used, camera frames
                                              * will be delivered as a raw framebuffer,
                                              * or as an OpenGL texture directly.
                                              *
                                              * The core has to tell the frontend here which types of
                                              * buffers can be handled properly.
                                              * An OpenGL texture can only be handled when using a
                                              * libretro GL core (SET_HW_RENDER).
                                              * It is recommended to use a libretro GL core when
                                              * using camera interface.
                                              *
                                              * The camera is not started automatically. The retrieved start/stop
                                              * functions must be used to explicitly
                                              * start and stop the camera driver.
                                              */
  #define RETRO_ENVIRONMENT_GET_LOG_INTERFACE 27
                                             /* struct retro_log_callback * --
                                              * Gets an interface for logging. This is useful for
                                              * logging in a cross-platform way
                                              * as certain platforms cannot use stderr for logging.
                                              * It also allows the frontend to
                                              * show logging information in a more suitable way.
                                              * If this interface is not used, libretro cores should
                                              * log to stderr as desired.
                                              */
  #define RETRO_ENVIRONMENT_GET_PERF_INTERFACE 28
                                             /* struct retro_perf_callback * --
                                              * Gets an interface for performance counters. This is useful
                                              * for performance logging in a cross-platform way and for detecting
                                              * architecture-specific features, such as SIMD support.
                                              */
  #define RETRO_ENVIRONMENT_GET_LOCATION_INTERFACE 29
                                             /* struct retro_location_callback * --
                                              * Gets access to the location interface.
                                              * The purpose of this interface is to be able to retrieve
                                              * location-based information from the host device,
                                              * such as current latitude / longitude.
                                              */
  #define RETRO_ENVIRONMENT_GET_CONTENT_DIRECTORY 30 /* Old name, kept for compatibility. */
  #define RETRO_ENVIRONMENT_GET_CORE_ASSETS_DIRECTORY 30
                                             /* const char ** --
                                              * Returns the "core assets" directory of the frontend.
                                              * This directory can be used to store specific assets that the
                                              * core relies upon, such as art assets,
                                              * input data, etc etc.
                                              * The returned value can be NULL.
                                              * If so, no such directory is defined,
                                              * and it's up to the implementation to find a suitable directory.
                                              */
  #define RETRO_ENVIRONMENT_GET_SAVE_DIRECTORY 31
                                             /* const char ** --
                                              * Returns the "save" directory of the frontend, unless there is no
                                              * save directory available. The save directory should be used to
                                              * store SRAM, memory cards, high scores, etc, if the libretro core
                                              * cannot use the regular memory interface (retro_get_memory_data()).
                                              *
                                              * If the frontend cannot designate a save directory, it will return
                                              * NULL to indicate that the core should attempt to operate without a
                                              * save directory set.
                                              *
                                              * NOTE: early libretro cores used the system directory for save
                                              * files. Cores that need to be backwards-compatible can still check
                                              * GET_SYSTEM_DIRECTORY.
                                              */
  #define RETRO_ENVIRONMENT_SET_SYSTEM_AV_INFO 32
                                             /* const struct retro_system_av_info * --
                                              * Sets a new av_info structure. This can only be called from
                                              * within retro_run().
                                              * This should *only* be used if the core is completely altering the
                                              * internal resolutions, aspect ratios, timings, sampling rate, etc.
                                              * Calling this can require a full reinitialization of video/audio
                                              * drivers in the frontend,
                                              *
                                              * so it is important to call it very sparingly, and usually only with
                                              * the users explicit consent.
                                              * An eventual driver reinitialize will happen so that video and
                                              * audio callbacks
                                              * happening after this call within the same retro_run() call will
                                              * target the newly initialized driver.
                                              *
                                              * This callback makes it possible to support configurable resolutions
                                              * in games, which can be useful to
                                              * avoid setting the "worst case" in max_width/max_height.
                                              *
                                              * ***HIGHLY RECOMMENDED*** Do not call this callback every time
                                              * resolution changes in an emulator core if it's
                                              * expected to be a temporary change, for the reasons of possible
                                              * driver reinitialization.
                                              * This call is not a free pass for not trying to provide
                                              * correct values in retro_get_system_av_info(). If you need to change
                                              * things like aspect ratio or nominal width/height,
                                              * use RETRO_ENVIRONMENT_SET_GEOMETRY, which is a softer variant
                                              * of SET_SYSTEM_AV_INFO.
                                              *
                                              * If this returns false, the frontend does not acknowledge a
                                              * changed av_info struct.
                                              */
  #define RETRO_ENVIRONMENT_SET_PROC_ADDRESS_CALLBACK 33
                                             /* const struct retro_get_proc_address_interface * --
                                              * Allows a libretro core to announce support for the
                                              * get_proc_address() interface.
                                              * This interface allows for a standard way to extend libretro where
                                              * use of environment calls are too indirect,
                                              * e.g. for cases where the frontend wants to call directly into the core.
                                              *
                                              * If a core wants to expose this interface, SET_PROC_ADDRESS_CALLBACK
                                              * **MUST** be called from within retro_set_environment().
                                              */
  #define RETRO_ENVIRONMENT_SET_SUBSYSTEM_INFO 34
                                             /* const struct retro_subsystem_info * --
                                              * This environment call introduces the concept of libretro "subsystems".
                                              * A subsystem is a variant of a libretro core which supports
                                              * different kinds of games.
                                              * The purpose of this is to support e.g. emulators which might
                                              * have special needs, e.g. Super Nintendo's Super GameBoy, Sufami Turbo.
                                              * It can also be used to pick among subsystems in an explicit way
                                              * if the libretro implementation is a multi-system emulator itself.
                                              *
                                              * Loading a game via a subsystem is done with retro_load_game_special(),
                                              * and this environment call allows a libretro core to expose which
                                              * subsystems are supported for use with retro_load_game_special().
                                              * A core passes an array of retro_game_special_info which is terminated
                                              * with a zeroed out retro_game_special_info struct.
                                              *
                                              * If a core wants to use this functionality, SET_SUBSYSTEM_INFO
                                              * **MUST** be called from within retro_set_environment().
                                              */
  #define RETRO_ENVIRONMENT_SET_CONTROLLER_INFO 35
                                             /* const struct retro_controller_info * --
                                              * This environment call lets a libretro core tell the frontend
                                              * which controller subclasses are recognized in calls to
                                              * retro_set_controller_port_device().
                                              *
                                              * Some emulators such as Super Nintendo support multiple lightgun
                                              * types which must be specifically selected from. It is therefore
                                              * sometimes necessary for a frontend to be able to tell the core
                                              * about a special kind of input device which is not specifcally
                                              * provided by the Libretro API.
                                              *
                                              * In order for a frontend to understand the workings of those devices,
                                              * they must be defined as a specialized subclass of the generic device
                                              * types already defined in the libretro API.
                                              *
                                              * The core must pass an array of const struct retro_controller_info which
                                              * is terminated with a blanked out struct. Each element of the
                                              * retro_controller_info struct corresponds to the ascending port index
                                              * that is passed to retro_set_controller_port_device() when that function
                                              * is called to indicate to the core that the frontend has changed the
                                              * active device subclass. SEE ALSO: retro_set_controller_port_device()
                                              *
                                              * The ascending input port indexes provided by the core in the struct
                                              * are generally presented by frontends as ascending User # or Player #,
                                              * such as Player 1, Player 2, Player 3, etc. Which device subclasses are
                                              * supported can vary per input port.
                                              *
                                              * The first inner element of each entry in the retro_controller_info array
                                              * is a retro_controller_description struct that specifies the names and
                                              * codes of all device subclasses that are available for the corresponding
                                              * User or Player, beginning with the generic Libretro device that the
                                              * subclasses are derived from. The second inner element of each entry is the
                                              * total number of subclasses that are listed in the retro_controller_description.
                                              *
                                              * NOTE: Even if special device types are set in the libretro core,
                                              * libretro should only poll input based on the base input device types.
                                              */
  #define RETRO_ENVIRONMENT_SET_MEMORY_MAPS (36 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* const struct retro_memory_map * --
                                              * This environment call lets a libretro core tell the frontend
                                              * about the memory maps this core emulates.
                                              * This can be used to implement, for example, cheats in a core-agnostic way.
                                              *
                                              * Should only be used by emulators; it doesn't make much sense for
                                              * anything else.
                                              * It is recommended to expose all relevant pointers through
                                              * retro_get_memory_* as well.
                                              *
                                              * Can be called from retro_init and retro_load_game.
                                              */
  #define RETRO_ENVIRONMENT_SET_GEOMETRY 37
                                             /* const struct retro_game_geometry * --
                                              * This environment call is similar to SET_SYSTEM_AV_INFO for changing
                                              * video parameters, but provides a guarantee that drivers will not be
                                              * reinitialized.
                                              * This can only be called from within retro_run().
                                              *
                                              * The purpose of this call is to allow a core to alter nominal
                                              * width/heights as well as aspect ratios on-the-fly, which can be
                                              * useful for some emulators to change in run-time.
                                              *
                                              * max_width/max_height arguments are ignored and cannot be changed
                                              * with this call as this could potentially require a reinitialization or a
                                              * non-constant time operation.
                                              * If max_width/max_height are to be changed, SET_SYSTEM_AV_INFO is required.
                                              *
                                              * A frontend must guarantee that this environment call completes in
                                              * constant time.
                                              */
  #define RETRO_ENVIRONMENT_GET_USERNAME 38
                                             /* const char **
                                              * Returns the specified username of the frontend, if specified by the user.
                                              * This username can be used as a nickname for a core that has online facilities
                                              * or any other mode where personalization of the user is desirable.
                                              * The returned value can be NULL.
                                              * If this environ callback is used by a core that requires a valid username,
                                              * a default username should be specified by the core.
                                              */
  #define RETRO_ENVIRONMENT_GET_LANGUAGE 39
                                             /* unsigned * --
                                              * Returns the specified language of the frontend, if specified by the user.
                                              * It can be used by the core for localization purposes.
                                              */
  #define RETRO_ENVIRONMENT_GET_CURRENT_SOFTWARE_FRAMEBUFFER (40 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_framebuffer * --
                                              * Returns a preallocated framebuffer which the core can use for rendering
                                              * the frame into when not using SET_HW_RENDER.
                                              * The framebuffer returned from this call must not be used
                                              * after the current call to retro_run() returns.
                                              *
                                              * The goal of this call is to allow zero-copy behavior where a core
                                              * can render directly into video memory, avoiding extra bandwidth cost by copying
                                              * memory from core to video memory.
                                              *
                                              * If this call succeeds and the core renders into it,
                                              * the framebuffer pointer and pitch can be passed to retro_video_refresh_t.
                                              * If the buffer from GET_CURRENT_SOFTWARE_FRAMEBUFFER is to be used,
                                              * the core must pass the exact
                                              * same pointer as returned by GET_CURRENT_SOFTWARE_FRAMEBUFFER;
                                              * i.e. passing a pointer which is offset from the
                                              * buffer is undefined. The width, height and pitch parameters
                                              * must also match exactly to the values obtained from GET_CURRENT_SOFTWARE_FRAMEBUFFER.
                                              *
                                              * It is possible for a frontend to return a different pixel format
                                              * than the one used in SET_PIXEL_FORMAT. This can happen if the frontend
                                              * needs to perform conversion.
                                              *
                                              * It is still valid for a core to render to a different buffer
                                              * even if GET_CURRENT_SOFTWARE_FRAMEBUFFER succeeds.
                                              *
                                              * A frontend must make sure that the pointer obtained from this function is
                                              * writeable (and readable).
                                              */
  #define RETRO_ENVIRONMENT_GET_HW_RENDER_INTERFACE (41 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* const struct retro_hw_render_interface ** --
                                              * Returns an API specific rendering interface for accessing API specific data.
                                              * Not all HW rendering APIs support or need this.
                                              * The contents of the returned pointer is specific to the rendering API
                                              * being used. See the various headers like libretro_vulkan.h, etc.
                                              *
                                              * GET_HW_RENDER_INTERFACE cannot be called before context_reset has been called.
                                              * Similarly, after context_destroyed callback returns,
                                              * the contents of the HW_RENDER_INTERFACE are invalidated.
                                              */
  #define RETRO_ENVIRONMENT_SET_SUPPORT_ACHIEVEMENTS (42 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* const bool * --
                                              * If true, the libretro implementation supports achievements
                                              * either via memory descriptors set with RETRO_ENVIRONMENT_SET_MEMORY_MAPS
                                              * or via retro_get_memory_data/retro_get_memory_size.
                                              *
                                              * This must be called before the first call to retro_run.
                                              */
  #define RETRO_ENVIRONMENT_SET_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE (43 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* const struct retro_hw_render_context_negotiation_interface * --
                                              * Sets an interface which lets the libretro core negotiate with frontend how a context is created.
                                              * The semantics of this interface depends on which API is used in SET_HW_RENDER earlier.
                                              * This interface will be used when the frontend is trying to create a HW rendering context,
                                              * so it will be used after SET_HW_RENDER, but before the context_reset callback.
                                              */
  #define RETRO_ENVIRONMENT_SET_SERIALIZATION_QUIRKS 44
                                             /* uint64_t * --
                                              * Sets quirk flags associated with serialization. The frontend will zero any flags it doesn't
                                              * recognize or support. Should be set in either retro_init or retro_load_game, but not both.
                                              */
  #define RETRO_ENVIRONMENT_SET_HW_SHARED_CONTEXT (44 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* N/A (null) * --
                                              * The frontend will try to use a 'shared' hardware context (mostly applicable
                                              * to OpenGL) when a hardware context is being set up.
                                              *
                                              * Returns true if the frontend supports shared hardware contexts and false
                                              * if the frontend does not support shared hardware contexts.
                                              *
                                              * This will do nothing on its own until SET_HW_RENDER env callbacks are
                                              * being used.
                                              */
  #define RETRO_ENVIRONMENT_GET_VFS_INTERFACE (45 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_vfs_interface_info * --
                                              * Gets access to the VFS interface.
                                              * VFS presence needs to be queried prior to load_game or any
                                              * get_system/save/other_directory being called to let front end know
                                              * core supports VFS before it starts handing out paths.
                                              * It is recomended to do so in retro_set_environment
                                              */
  #define RETRO_ENVIRONMENT_GET_LED_INTERFACE (46 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_led_interface * --
                                              * Gets an interface which is used by a libretro core to set
                                              * state of LEDs.
                                              */
  #define RETRO_ENVIRONMENT_GET_AUDIO_VIDEO_ENABLE (47 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* int * --
                                              * Tells the core if the frontend wants audio or video.
                                              * If disabled, the frontend will discard the audio or video,
                                              * so the core may decide to skip generating a frame or generating audio.
                                              * This is mainly used for increasing performance.
                                              * Bit 0 (value 1): Enable Video
                                              * Bit 1 (value 2): Enable Audio
                                              * Bit 2 (value 4): Use Fast Savestates.
                                              * Bit 3 (value 8): Hard Disable Audio
                                              * Other bits are reserved for future use and will default to zero.
                                              * If video is disabled:
                                              * * The frontend wants the core to not generate any video,
                                              *   including presenting frames via hardware acceleration.
                                              * * The frontend's video frame callback will do nothing.
                                              * * After running the frame, the video output of the next frame should be
                                              *   no different than if video was enabled, and saving and loading state
                                              *   should have no issues.
                                              * If audio is disabled:
                                              * * The frontend wants the core to not generate any audio.
                                              * * The frontend's audio callbacks will do nothing.
                                              * * After running the frame, the audio output of the next frame should be
                                              *   no different than if audio was enabled, and saving and loading state
                                              *   should have no issues.
                                              * Fast Savestates:
                                              * * Guaranteed to be created by the same binary that will load them.
                                              * * Will not be written to or read from the disk.
                                              * * Suggest that the core assumes loading state will succeed.
                                              * * Suggest that the core updates its memory buffers in-place if possible.
                                              * * Suggest that the core skips clearing memory.
                                              * * Suggest that the core skips resetting the system.
                                              * * Suggest that the core may skip validation steps.
                                              * Hard Disable Audio:
                                              * * Used for a secondary core when running ahead.
                                              * * Indicates that the frontend will never need audio from the core.
                                              * * Suggests that the core may stop synthesizing audio, but this should not
                                              *   compromise emulation accuracy.
                                              * * Audio output for the next frame does not matter, and the frontend will
                                              *   never need an accurate audio state in the future.
                                              * * State will never be saved when using Hard Disable Audio.
                                              */
  #define RETRO_ENVIRONMENT_GET_MIDI_INTERFACE (48 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_midi_interface ** --
                                              * Returns a MIDI interface that can be used for raw data I/O.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_FASTFORWARDING (49 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                              /* bool * --
                                              * Boolean value that indicates whether or not the frontend is in
                                              * fastforwarding mode.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_TARGET_REFRESH_RATE (50 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                              /* float * --
                                              * Float value that lets us know what target refresh rate
                                              * is curently in use by the frontend.
                                              *
                                              * The core can use the returned value to set an ideal
                                              * refresh rate/framerate.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_INPUT_BITMASKS (51 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                              /* bool * --
                                              * Boolean value that indicates whether or not the frontend supports
                                              * input bitmasks being returned by retro_input_state_t. The advantage
                                              * of this is that retro_input_state_t has to be only called once to
                                              * grab all button states instead of multiple times.
                                              *
                                              * If it returns true, you can pass RETRO_DEVICE_ID_JOYPAD_MASK as 'id'
                                              * to retro_input_state_t (make sure 'device' is set to RETRO_DEVICE_JOYPAD).
                                              * It will return a bitmask of all the digital buttons.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION 52
                                             /* unsigned * --
                                              * Unsigned value is the API version number of the core options
                                              * interface supported by the frontend. If callback return false,
                                              * API version is assumed to be 0.
                                              *
                                              * In legacy code, core options are set by passing an array of
                                              * retro_variable structs to RETRO_ENVIRONMENT_SET_VARIABLES.
                                              * This may be still be done regardless of the core options
                                              * interface version.
                                              *
                                              * If version is >= 1 however, core options may instead be set by
                                              * passing an array of retro_core_option_definition structs to
                                              * RETRO_ENVIRONMENT_SET_CORE_OPTIONS, or a 2D array of
                                              * retro_core_option_definition structs to RETRO_ENVIRONMENT_SET_CORE_OPTIONS_INTL.
                                              * This allows the core to additionally set option sublabel information
                                              * and/or provide localisation support.
                                              *
                                              * If version is >= 2, core options may instead be set by passing
                                              * a retro_core_options_v2 struct to RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2,
                                              * or an array of retro_core_options_v2 structs to
                                              * RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2_INTL. This allows the core
                                              * to additionally set optional core option category information
                                              * for frontends with core option category support.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS 53
                                             /* const struct retro_core_option_definition ** --
                                              * Allows an implementation to signal the environment
                                              * which variables it might want to check for later using
                                              * GET_VARIABLE.
                                              * This allows the frontend to present these variables to
                                              * a user dynamically.
                                              * This should only be called if RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION
                                              * returns an API version of >= 1.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_VARIABLES.
                                              * This should be called the first time as early as
                                              * possible (ideally in retro_set_environment).
                                              * Afterwards it may be called again for the core to communicate
                                              * updated options to the frontend, but the number of core
                                              * options must not change from the number in the initial call.
                                              *
                                              * 'data' points to an array of retro_core_option_definition structs
                                              * terminated by a { NULL, NULL, NULL, {{0}}, NULL } element.
                                              * retro_core_option_definition::key should be namespaced to not collide
                                              * with other implementations' keys. e.g. A core called
                                              * 'foo' should use keys named as 'foo_option'.
                                              * retro_core_option_definition::desc should contain a human readable
                                              * description of the key.
                                              * retro_core_option_definition::info should contain any additional human
                                              * readable information text that a typical user may need to
                                              * understand the functionality of the option.
                                              * retro_core_option_definition::values is an array of retro_core_option_value
                                              * structs terminated by a { NULL, NULL } element.
                                              * > retro_core_option_definition::values[index].value is an expected option
                                              *   value.
                                              * > retro_core_option_definition::values[index].label is a human readable
                                              *   label used when displaying the value on screen. If NULL,
                                              *   the value itself is used.
                                              * retro_core_option_definition::default_value is the default core option
                                              * setting. It must match one of the expected option values in the
                                              * retro_core_option_definition::values array. If it does not, or the
                                              * default value is NULL, the first entry in the
                                              * retro_core_option_definition::values array is treated as the default.
                                              *
                                              * The number of possible option values should be very limited,
                                              * and must be less than RETRO_NUM_CORE_OPTION_VALUES_MAX.
                                              * i.e. it should be feasible to cycle through options
                                              * without a keyboard.
                                              *
                                              * Example entry:
                                              * {
                                              *     "foo_option",
                                              *     "Speed hack coprocessor X",
                                              *     "Provides increased performance at the expense of reduced accuracy",
                                              * 	  {
                                              *         { "false",    NULL },
                                              *         { "true",     NULL },
                                              *         { "unstable", "Turbo (Unstable)" },
                                              *         { NULL, NULL },
                                              *     },
                                              *     "false"
                                              * }
                                              *
                                              * Only strings are operated on. The possible values will
                                              * generally be displayed and stored as-is by the frontend.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS_INTL 54
                                             /* const struct retro_core_options_intl * --
                                              * Allows an implementation to signal the environment
                                              * which variables it might want to check for later using
                                              * GET_VARIABLE.
                                              * This allows the frontend to present these variables to
                                              * a user dynamically.
                                              * This should only be called if RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION
                                              * returns an API version of >= 1.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_VARIABLES.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_CORE_OPTIONS.
                                              * This should be called the first time as early as
                                              * possible (ideally in retro_set_environment).
                                              * Afterwards it may be called again for the core to communicate
                                              * updated options to the frontend, but the number of core
                                              * options must not change from the number in the initial call.
                                              *
                                              * This is fundamentally the same as RETRO_ENVIRONMENT_SET_CORE_OPTIONS,
                                              * with the addition of localisation support. The description of the
                                              * RETRO_ENVIRONMENT_SET_CORE_OPTIONS callback should be consulted
                                              * for further details.
                                              *
                                              * 'data' points to a retro_core_options_intl struct.
                                              *
                                              * retro_core_options_intl::us is a pointer to an array of
                                              * retro_core_option_definition structs defining the US English
                                              * core options implementation. It must point to a valid array.
                                              *
                                              * retro_core_options_intl::local is a pointer to an array of
                                              * retro_core_option_definition structs defining core options for
                                              * the current frontend language. It may be NULL (in which case
                                              * retro_core_options_intl::us is used by the frontend). Any items
                                              * missing from this array will be read from retro_core_options_intl::us
                                              * instead.
                                              *
                                              * NOTE: Default core option values are always taken from the
                                              * retro_core_options_intl::us array. Any default values in
                                              * retro_core_options_intl::local array will be ignored.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS_DISPLAY 55
                                             /* struct retro_core_option_display * --
                                              *
                                              * Allows an implementation to signal the environment to show
                                              * or hide a variable when displaying core options. This is
                                              * considered a *suggestion*. The frontend is free to ignore
                                              * this callback, and its implementation not considered mandatory.
                                              *
                                              * 'data' points to a retro_core_option_display struct
                                              *
                                              * retro_core_option_display::key is a variable identifier
                                              * which has already been set by SET_VARIABLES/SET_CORE_OPTIONS.
                                              *
                                              * retro_core_option_display::visible is a boolean, specifying
                                              * whether variable should be displayed
                                              *
                                              * Note that all core option variables will be set visible by
                                              * default when calling SET_VARIABLES/SET_CORE_OPTIONS.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_PREFERRED_HW_RENDER 56
                                             /* unsigned * --
                                              *
                                              * Allows an implementation to ask frontend preferred hardware
                                              * context to use. Core should use this information to deal
                                              * with what specific context to request with SET_HW_RENDER.
                                              *
                                              * 'data' points to an unsigned variable
                                              */
  
  #define RETRO_ENVIRONMENT_GET_DISK_CONTROL_INTERFACE_VERSION 57
                                             /* unsigned * --
                                              * Unsigned value is the API version number of the disk control
                                              * interface supported by the frontend. If callback return false,
                                              * API version is assumed to be 0.
                                              *
                                              * In legacy code, the disk control interface is defined by passing
                                              * a struct of type retro_disk_control_callback to
                                              * RETRO_ENVIRONMENT_SET_DISK_CONTROL_INTERFACE.
                                              * This may be still be done regardless of the disk control
                                              * interface version.
                                              *
                                              * If version is >= 1 however, the disk control interface may
                                              * instead be defined by passing a struct of type
                                              * retro_disk_control_ext_callback to
                                              * RETRO_ENVIRONMENT_SET_DISK_CONTROL_EXT_INTERFACE.
                                              * This allows the core to provide additional information about
                                              * disk images to the frontend and/or enables extra
                                              * disk control functionality by the frontend.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_DISK_CONTROL_EXT_INTERFACE 58
                                             /* const struct retro_disk_control_ext_callback * --
                                              * Sets an interface which frontend can use to eject and insert
                                              * disk images, and also obtain information about individual
                                              * disk image files registered by the core.
                                              * This is used for games which consist of multiple images and
                                              * must be manually swapped out by the user (e.g. PSX, floppy disk
                                              * based systems).
                                              */
  
  #define RETRO_ENVIRONMENT_GET_MESSAGE_INTERFACE_VERSION 59
                                             /* unsigned * --
                                              * Unsigned value is the API version number of the message
                                              * interface supported by the frontend. If callback returns
                                              * false, API version is assumed to be 0.
                                              *
                                              * In legacy code, messages may be displayed in an
                                              * implementation-specific manner by passing a struct
                                              * of type retro_message to RETRO_ENVIRONMENT_SET_MESSAGE.
                                              * This may be still be done regardless of the message
                                              * interface version.
                                              *
                                              * If version is >= 1 however, messages may instead be
                                              * displayed by passing a struct of type retro_message_ext
                                              * to RETRO_ENVIRONMENT_SET_MESSAGE_EXT. This allows the
                                              * core to specify message logging level, priority and
                                              * destination (OSD, logging interface or both).
                                              */
  
  #define RETRO_ENVIRONMENT_SET_MESSAGE_EXT 60
                                             /* const struct retro_message_ext * --
                                              * Sets a message to be displayed in an implementation-specific
                                              * manner for a certain amount of 'frames'. Additionally allows
                                              * the core to specify message logging level, priority and
                                              * destination (OSD, logging interface or both).
                                              * Should not be used for trivial messages, which should simply be
                                              * logged via RETRO_ENVIRONMENT_GET_LOG_INTERFACE (or as a
                                              * fallback, stderr).
                                              */
  
  #define RETRO_ENVIRONMENT_GET_INPUT_MAX_USERS 61
                                             /* unsigned * --
                                              * Unsigned value is the number of active input devices
                                              * provided by the frontend. This may change between
                                              * frames, but will remain constant for the duration
                                              * of each frame.
                                              * If callback returns true, a core need not poll any
                                              * input device with an index greater than or equal to
                                              * the number of active devices.
                                              * If callback returns false, the number of active input
                                              * devices is unknown. In this case, all input devices
                                              * should be considered active.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_AUDIO_BUFFER_STATUS_CALLBACK 62
                                             /* const struct retro_audio_buffer_status_callback * --
                                              * Lets the core know the occupancy level of the frontend
                                              * audio buffer. Can be used by a core to attempt frame
                                              * skipping in order to avoid buffer under-runs.
                                              * A core may pass NULL to disable buffer status reporting
                                              * in the frontend.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_MINIMUM_AUDIO_LATENCY 63
                                             /* const unsigned * --
                                              * Sets minimum frontend audio latency in milliseconds.
                                              * Resultant audio latency may be larger than set value,
                                              * or smaller if a hardware limit is encountered. A frontend
                                              * is expected to honour requests up to 512 ms.
                                              *
                                              * - If value is less than current frontend
                                              *   audio latency, callback has no effect
                                              * - If value is zero, default frontend audio
                                              *   latency is set
                                              *
                                              * May be used by a core to increase audio latency and
                                              * therefore decrease the probability of buffer under-runs
                                              * (crackling) when performing 'intensive' operations.
                                              * A core utilising RETRO_ENVIRONMENT_SET_AUDIO_BUFFER_STATUS_CALLBACK
                                              * to implement audio-buffer-based frame skipping may achieve
                                              * optimal results by setting the audio latency to a 'high'
                                              * (typically 6x or 8x) integer multiple of the expected
                                              * frame time.
                                              *
                                              * WARNING: This can only be called from within retro_run().
                                              * Calling this can require a full reinitialization of audio
                                              * drivers in the frontend, so it is important to call it very
                                              * sparingly, and usually only with the users explicit consent.
                                              * An eventual driver reinitialize will happen so that audio
                                              * callbacks happening after this call within the same retro_run()
                                              * call will target the newly initialized driver.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_FASTFORWARDING_OVERRIDE 64
                                             /* const struct retro_fastforwarding_override * --
                                              * Used by a libretro core to override the current
                                              * fastforwarding mode of the frontend.
                                              * If NULL is passed to this function, the frontend
                                              * will return true if fastforwarding override
                                              * functionality is supported (no change in
                                              * fastforwarding state will occur in this case).
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CONTENT_INFO_OVERRIDE 65
                                             /* const struct retro_system_content_info_override * --
                                              * Allows an implementation to override 'global' content
                                              * info parameters reported by retro_get_system_info().
                                              * Overrides also affect subsystem content info parameters
                                              * set via RETRO_ENVIRONMENT_SET_SUBSYSTEM_INFO.
                                              * This function must be called inside retro_set_environment().
                                              * If callback returns false, content info overrides
                                              * are unsupported by the frontend, and will be ignored.
                                              * If callback returns true, extended game info may be
                                              * retrieved by calling RETRO_ENVIRONMENT_GET_GAME_INFO_EXT
                                              * in retro_load_game() or retro_load_game_special().
                                              *
                                              * 'data' points to an array of retro_system_content_info_override
                                              * structs terminated by a { NULL, false, false } element.
                                              * If 'data' is NULL, no changes will be made to the frontend;
                                              * a core may therefore pass NULL in order to test whether
                                              * the RETRO_ENVIRONMENT_SET_CONTENT_INFO_OVERRIDE and
                                              * RETRO_ENVIRONMENT_GET_GAME_INFO_EXT callbacks are supported
                                              * by the frontend.
                                              *
                                              * For struct member descriptions, see the definition of
                                              * struct retro_system_content_info_override.
                                              *
                                              * Example:
                                              *
                                              * - struct retro_system_info:
                                              * {
                                              *    "My Core",                      // library_name
                                              *    "v1.0",                         // library_version
                                              *    "m3u|md|cue|iso|chd|sms|gg|sg", // valid_extensions
                                              *    true,                           // need_fullpath
                                              *    false                           // block_extract
                                              * }
                                              *
                                              * - Array of struct retro_system_content_info_override:
                                              * {
                                              *    {
                                              *       "md|sms|gg", // extensions
                                              *       false,       // need_fullpath
                                              *       true         // persistent_data
                                              *    },
                                              *    {
                                              *       "sg",        // extensions
                                              *       false,       // need_fullpath
                                              *       false        // persistent_data
                                              *    },
                                              *    { NULL, false, false }
                                              * }
                                              *
                                              * Result:
                                              * - Files of type m3u, cue, iso, chd will not be
                                              *   loaded by the frontend. Frontend will pass a
                                              *   valid path to the core, and core will handle
                                              *   loading internally
                                              * - Files of type md, sms, gg will be loaded by
                                              *   the frontend. A valid memory buffer will be
                                              *   passed to the core. This memory buffer will
                                              *   remain valid until retro_deinit() returns
                                              * - Files of type sg will be loaded by the frontend.
                                              *   A valid memory buffer will be passed to the core.
                                              *   This memory buffer will remain valid until
                                              *   retro_load_game() (or retro_load_game_special())
                                              *   returns
                                              *
                                              * NOTE: If an extension is listed multiple times in
                                              * an array of retro_system_content_info_override
                                              * structs, only the first instance will be registered
                                              */
  
  #define RETRO_ENVIRONMENT_GET_GAME_INFO_EXT 66
                                             /* const struct retro_game_info_ext ** --
                                              * Allows an implementation to fetch extended game
                                              * information, providing additional content path
                                              * and memory buffer status details.
                                              * This function may only be called inside
                                              * retro_load_game() or retro_load_game_special().
                                              * If callback returns false, extended game information
                                              * is unsupported by the frontend. In this case, only
                                              * regular retro_game_info will be available.
                                              * RETRO_ENVIRONMENT_GET_GAME_INFO_EXT is guaranteed
                                              * to return true if RETRO_ENVIRONMENT_SET_CONTENT_INFO_OVERRIDE
                                              * returns true.
                                              *
                                              * 'data' points to an array of retro_game_info_ext structs.
                                              *
                                              * For struct member descriptions, see the definition of
                                              * struct retro_game_info_ext.
                                              *
                                              * - If function is called inside retro_load_game(),
                                              *   the retro_game_info_ext array is guaranteed to
                                              *   have a size of 1 - i.e. the returned pointer may
                                              *   be used to access directly the members of the
                                              *   first retro_game_info_ext struct, for example:
                                              *
                                              *      struct retro_game_info_ext *game_info_ext;
                                              *      if (environ_cb(RETRO_ENVIRONMENT_GET_GAME_INFO_EXT, &game_info_ext))
                                              *         printf("Content Directory: %s\n", game_info_ext->dir);
                                              *
                                              * - If the function is called inside retro_load_game_special(),
                                              *   the retro_game_info_ext array is guaranteed to have a
                                              *   size equal to the num_info argument passed to
                                              *   retro_load_game_special()
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2 67
                                             /* const struct retro_core_options_v2 * --
                                              * Allows an implementation to signal the environment
                                              * which variables it might want to check for later using
                                              * GET_VARIABLE.
                                              * This allows the frontend to present these variables to
                                              * a user dynamically.
                                              * This should only be called if RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION
                                              * returns an API version of >= 2.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_VARIABLES.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_CORE_OPTIONS.
                                              * This should be called the first time as early as
                                              * possible (ideally in retro_set_environment).
                                              * Afterwards it may be called again for the core to communicate
                                              * updated options to the frontend, but the number of core
                                              * options must not change from the number in the initial call.
                                              * If RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION returns an API
                                              * version of >= 2, this callback is guaranteed to succeed
                                              * (i.e. callback return value does not indicate success)
                                              * If callback returns true, frontend has core option category
                                              * support.
                                              * If callback returns false, frontend does not have core option
                                              * category support.
                                              *
                                              * 'data' points to a retro_core_options_v2 struct, containing
                                              * of two pointers:
                                              * - retro_core_options_v2::categories is an array of
                                              *   retro_core_option_v2_category structs terminated by a
                                              *   { NULL, NULL, NULL } element. If retro_core_options_v2::categories
                                              *   is NULL, all core options will have no category and will be shown
                                              *   at the top level of the frontend core option interface. If frontend
                                              *   does not have core option category support, categories array will
                                              *   be ignored.
                                              * - retro_core_options_v2::definitions is an array of
                                              *   retro_core_option_v2_definition structs terminated by a
                                              *   { NULL, NULL, NULL, NULL, NULL, NULL, {{0}}, NULL }
                                              *   element.
                                              *
                                              * >> retro_core_option_v2_category notes:
                                              *
                                              * - retro_core_option_v2_category::key should contain string
                                              *   that uniquely identifies the core option category. Valid
                                              *   key characters are [a-z, A-Z, 0-9, _, -]
                                              *   Namespace collisions with other implementations' category
                                              *   keys are permitted.
                                              * - retro_core_option_v2_category::desc should contain a human
                                              *   readable description of the category key.
                                              * - retro_core_option_v2_category::info should contain any
                                              *   additional human readable information text that a typical
                                              *   user may need to understand the nature of the core option
                                              *   category.
                                              *
                                              * Example entry:
                                              * {
                                              *     "advanced_settings",
                                              *     "Advanced",
                                              *     "Options affecting low-level emulation performance and accuracy."
                                              * }
                                              *
                                              * >> retro_core_option_v2_definition notes:
                                              *
                                              * - retro_core_option_v2_definition::key should be namespaced to not
                                              *   collide with other implementations' keys. e.g. A core called
                                              *   'foo' should use keys named as 'foo_option'. Valid key characters
                                              *   are [a-z, A-Z, 0-9, _, -].
                                              * - retro_core_option_v2_definition::desc should contain a human readable
                                              *   description of the key. Will be used when the frontend does not
                                              *   have core option category support. Examples: "Aspect Ratio" or
                                              *   "Video > Aspect Ratio".
                                              * - retro_core_option_v2_definition::desc_categorized should contain a
                                              *   human readable description of the key, which will be used when
                                              *   frontend has core option category support. Example: "Aspect Ratio",
                                              *   where associated retro_core_option_v2_category::desc is "Video".
                                              *   If empty or NULL, the string specified by
                                              *   retro_core_option_v2_definition::desc will be used instead.
                                              *   retro_core_option_v2_definition::desc_categorized will be ignored
                                              *   if retro_core_option_v2_definition::category_key is empty or NULL.
                                              * - retro_core_option_v2_definition::info should contain any additional
                                              *   human readable information text that a typical user may need to
                                              *   understand the functionality of the option.
                                              * - retro_core_option_v2_definition::info_categorized should contain
                                              *   any additional human readable information text that a typical user
                                              *   may need to understand the functionality of the option, and will be
                                              *   used when frontend has core option category support. This is provided
                                              *   to accommodate the case where info text references an option by
                                              *   name/desc, and the desc/desc_categorized text for that option differ.
                                              *   If empty or NULL, the string specified by
                                              *   retro_core_option_v2_definition::info will be used instead.
                                              *   retro_core_option_v2_definition::info_categorized will be ignored
                                              *   if retro_core_option_v2_definition::category_key is empty or NULL.
                                              * - retro_core_option_v2_definition::category_key should contain a
                                              *   category identifier (e.g. "video" or "audio") that will be
                                              *   assigned to the core option if frontend has core option category
                                              *   support. A categorized option will be shown in a subsection/
                                              *   submenu of the frontend core option interface. If key is empty
                                              *   or NULL, or if key does not match one of the
                                              *   retro_core_option_v2_category::key values in the associated
                                              *   retro_core_option_v2_category array, option will have no category
                                              *   and will be shown at the top level of the frontend core option
                                              *   interface.
                                              * - retro_core_option_v2_definition::values is an array of
                                              *   retro_core_option_value structs terminated by a { NULL, NULL }
                                              *   element.
                                              * --> retro_core_option_v2_definition::values[index].value is an
                                              *     expected option value.
                                              * --> retro_core_option_v2_definition::values[index].label is a
                                              *     human readable label used when displaying the value on screen.
                                              *     If NULL, the value itself is used.
                                              * - retro_core_option_v2_definition::default_value is the default
                                              *   core option setting. It must match one of the expected option
                                              *   values in the retro_core_option_v2_definition::values array. If
                                              *   it does not, or the default value is NULL, the first entry in the
                                              *   retro_core_option_v2_definition::values array is treated as the
                                              *   default.
                                              *
                                              * The number of possible option values should be very limited,
                                              * and must be less than RETRO_NUM_CORE_OPTION_VALUES_MAX.
                                              * i.e. it should be feasible to cycle through options
                                              * without a keyboard.
                                              *
                                              * Example entries:
                                              *
                                              * - Uncategorized:
                                              *
                                              * {
                                              *     "foo_option",
                                              *     "Speed hack coprocessor X",
                                              *     NULL,
                                              *     "Provides increased performance at the expense of reduced accuracy.",
                                              *     NULL,
                                              *     NULL,
                                              * 	  {
                                              *         { "false",    NULL },
                                              *         { "true",     NULL },
                                              *         { "unstable", "Turbo (Unstable)" },
                                              *         { NULL, NULL },
                                              *     },
                                              *     "false"
                                              * }
                                              *
                                              * - Categorized:
                                              *
                                              * {
                                              *     "foo_option",
                                              *     "Advanced > Speed hack coprocessor X",
                                              *     "Speed hack coprocessor X",
                                              *     "Setting 'Advanced > Speed hack coprocessor X' to 'true' or 'Turbo' provides increased performance at the expense of reduced accuracy",
                                              *     "Setting 'Speed hack coprocessor X' to 'true' or 'Turbo' provides increased performance at the expense of reduced accuracy",
                                              *     "advanced_settings",
                                              * 	  {
                                              *         { "false",    NULL },
                                              *         { "true",     NULL },
                                              *         { "unstable", "Turbo (Unstable)" },
                                              *         { NULL, NULL },
                                              *     },
                                              *     "false"
                                              * }
                                              *
                                              * Only strings are operated on. The possible values will
                                              * generally be displayed and stored as-is by the frontend.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2_INTL 68
                                             /* const struct retro_core_options_v2_intl * --
                                              * Allows an implementation to signal the environment
                                              * which variables it might want to check for later using
                                              * GET_VARIABLE.
                                              * This allows the frontend to present these variables to
                                              * a user dynamically.
                                              * This should only be called if RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION
                                              * returns an API version of >= 2.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_VARIABLES.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_CORE_OPTIONS.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_CORE_OPTIONS_INTL.
                                              * This should be called instead of RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2.
                                              * This should be called the first time as early as
                                              * possible (ideally in retro_set_environment).
                                              * Afterwards it may be called again for the core to communicate
                                              * updated options to the frontend, but the number of core
                                              * options must not change from the number in the initial call.
                                              * If RETRO_ENVIRONMENT_GET_CORE_OPTIONS_VERSION returns an API
                                              * version of >= 2, this callback is guaranteed to succeed
                                              * (i.e. callback return value does not indicate success)
                                              * If callback returns true, frontend has core option category
                                              * support.
                                              * If callback returns false, frontend does not have core option
                                              * category support.
                                              *
                                              * This is fundamentally the same as RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2,
                                              * with the addition of localisation support. The description of the
                                              * RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2 callback should be consulted
                                              * for further details.
                                              *
                                              * 'data' points to a retro_core_options_v2_intl struct.
                                              *
                                              * - retro_core_options_v2_intl::us is a pointer to a
                                              *   retro_core_options_v2 struct defining the US English
                                              *   core options implementation. It must point to a valid struct.
                                              *
                                              * - retro_core_options_v2_intl::local is a pointer to a
                                              *   retro_core_options_v2 struct defining core options for
                                              *   the current frontend language. It may be NULL (in which case
                                              *   retro_core_options_v2_intl::us is used by the frontend). Any items
                                              *   missing from this struct will be read from
                                              *   retro_core_options_v2_intl::us instead.
                                              *
                                              * NOTE: Default core option values are always taken from the
                                              * retro_core_options_v2_intl::us struct. Any default values in
                                              * the retro_core_options_v2_intl::local struct will be ignored.
                                              */
  
  #define RETRO_ENVIRONMENT_SET_CORE_OPTIONS_UPDATE_DISPLAY_CALLBACK 69
                                             /* const struct retro_core_options_update_display_callback * --
                                              * Allows a frontend to signal that a core must update
                                              * the visibility of any dynamically hidden core options,
                                              * and enables the frontend to detect visibility changes.
                                              * Used by the frontend to update the menu display status
                                              * of core options without requiring a call of retro_run().
                                              * Must be called in retro_set_environment().
                                              */
  
  #define RETRO_ENVIRONMENT_SET_VARIABLE 70
                                             /* const struct retro_variable * --
                                              * Allows an implementation to notify the frontend
                                              * that a core option value has changed.
                                              *
                                              * retro_variable::key and retro_variable::value
                                              * must match strings that have been set previously
                                              * via one of the following:
                                              *
                                              * - RETRO_ENVIRONMENT_SET_VARIABLES
                                              * - RETRO_ENVIRONMENT_SET_CORE_OPTIONS
                                              * - RETRO_ENVIRONMENT_SET_CORE_OPTIONS_INTL
                                              * - RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2
                                              * - RETRO_ENVIRONMENT_SET_CORE_OPTIONS_V2_INTL
                                              *
                                              * After changing a core option value via this
                                              * callback, RETRO_ENVIRONMENT_GET_VARIABLE_UPDATE
                                              * will return true.
                                              *
                                              * If data is NULL, no changes will be registered
                                              * and the callback will return true; an
                                              * implementation may therefore pass NULL in order
                                              * to test whether the callback is supported.
                                              */
  
  #define RETRO_ENVIRONMENT_GET_THROTTLE_STATE (71 | RETRO_ENVIRONMENT_EXPERIMENTAL)
                                             /* struct retro_throttle_state * --
                                              * Allows an implementation to get details on the actual rate
                                              * the frontend is attempting to call retro_run().
                                              */
  
  /* VFS functionality */
  
  /* File paths:
   * File paths passed as parameters when using this API shall be well formed UNIX-style,
   * using "/" (unquoted forward slash) as directory separator regardless of the platform's native separator.
   * Paths shall also include at least one forward slash ("game.bin" is an invalid path, use "./game.bin" instead).
   * Other than the directory separator, cores shall not make assumptions about path format:
   * "C:/path/game.bin", "http://example.com/game.bin", "#game/game.bin", "./game.bin" (without quotes) are all valid paths.
   * Cores may replace the basename or remove path components from the end, and/or add new components;
   * however, cores shall not append "./", "../" or multiple consecutive forward slashes ("//") to paths they request to front end.
   * The frontend is encouraged to make such paths work as well as it can, but is allowed to give up if the core alters paths too much.
   * Frontends are encouraged, but not required, to support native file system paths (modulo replacing the directory separator, if applicable).
   * Cores are allowed to try using them, but must remain functional if the front rejects such requests.
   * Cores are encouraged to use the libretro-common filestream functions for file I/O,
   * as they seamlessly integrate with VFS, deal with directory separator replacement as appropriate
   * and provide platform-specific fallbacks in cases where front ends do not support VFS. */
  
  /* Opaque file handle
   * Introduced in VFS API v1 */
  struct retro_vfs_file_handle;
  
  /* Opaque directory handle
   * Introduced in VFS API v3 */
  struct retro_vfs_dir_handle;
  
  /* File open flags
   * Introduced in VFS API v1 */
  #define RETRO_VFS_FILE_ACCESS_READ            (1 << 0) /* Read only mode */
  #define RETRO_VFS_FILE_ACCESS_WRITE           (1 << 1) /* Write only mode, discard contents and overwrites existing file unless RETRO_VFS_FILE_ACCESS_UPDATE is also specified */
  #define RETRO_VFS_FILE_ACCESS_READ_WRITE      (RETRO_VFS_FILE_ACCESS_READ | RETRO_VFS_FILE_ACCESS_WRITE) /* Read-write mode, discard contents and overwrites existing file unless RETRO_VFS_FILE_ACCESS_UPDATE is also specified*/
  #define RETRO_VFS_FILE_ACCESS_UPDATE_EXISTING (1 << 2) /* Prevents discarding content of existing files opened for writing */
  
  /* These are only hints. The frontend may choose to ignore them. Other than RAM/CPU/etc use,
     and how they react to unlikely external interference (for example someone else writing to that file,
     or the file's server going down), behavior will not change. */
  #define RETRO_VFS_FILE_ACCESS_HINT_NONE              (0)
  /* Indicate that the file will be accessed many times. The frontend should aggressively cache everything. */
  #define RETRO_VFS_FILE_ACCESS_HINT_FREQUENT_ACCESS   (1 << 0)
  
  /* Seek positions */
  #define RETRO_VFS_SEEK_POSITION_START    0
  #define RETRO_VFS_SEEK_POSITION_CURRENT  1
  #define RETRO_VFS_SEEK_POSITION_END      2
  
  /* stat() result flags
   * Introduced in VFS API v3 */
  #define RETRO_VFS_STAT_IS_VALID               (1 << 0)
  #define RETRO_VFS_STAT_IS_DIRECTORY           (1 << 1)
  #define RETRO_VFS_STAT_IS_CHARACTER_SPECIAL   (1 << 2)
  
  /* Get path from opaque handle. Returns the exact same path passed to file_open when getting the handle
   * Introduced in VFS API v1 */
  typedef const char *(RETRO_CALLCONV *retro_vfs_get_path_t)(struct retro_vfs_file_handle *stream);
  
  /* Open a file for reading or writing. If path points to a directory, this will
   * fail. Returns the opaque file handle, or NULL for error.
   * Introduced in VFS API v1 */
  typedef struct retro_vfs_file_handle *(RETRO_CALLCONV *retro_vfs_open_t)(const char *path, unsigned mode, unsigned hints);
  
  /* Close the file and release its resources. Must be called if open_file returns non-NULL. Returns 0 on success, -1 on failure.
   * Whether the call succeeds ot not, the handle passed as parameter becomes invalid and should no longer be used.
   * Introduced in VFS API v1 */
  typedef int (RETRO_CALLCONV *retro_vfs_close_t)(struct retro_vfs_file_handle *stream);
  
  /* Return the size of the file in bytes, or -1 for error.
   * Introduced in VFS API v1 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_size_t)(struct retro_vfs_file_handle *stream);
  
  /* Truncate file to specified size. Returns 0 on success or -1 on error
   * Introduced in VFS API v2 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_truncate_t)(struct retro_vfs_file_handle *stream, int64_t length);
  
  /* Get the current read / write position for the file. Returns -1 for error.
   * Introduced in VFS API v1 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_tell_t)(struct retro_vfs_file_handle *stream);
  
  /* Set the current read/write position for the file. Returns the new position, -1 for error.
   * Introduced in VFS API v1 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_seek_t)(struct retro_vfs_file_handle *stream, int64_t offset, int seek_position);
  
  /* Read data from a file. Returns the number of bytes read, or -1 for error.
   * Introduced in VFS API v1 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_read_t)(struct retro_vfs_file_handle *stream, void *s, uint64_t len);
  
  /* Write data to a file. Returns the number of bytes written, or -1 for error.
   * Introduced in VFS API v1 */
  typedef int64_t (RETRO_CALLCONV *retro_vfs_write_t)(struct retro_vfs_file_handle *stream, const void *s, uint64_t len);
  
  /* Flush pending writes to file, if using buffered IO. Returns 0 on sucess, or -1 on failure.
   * Introduced in VFS API v1 */
  typedef int (RETRO_CALLCONV *retro_vfs_flush_t)(struct retro_vfs_file_handle *stream);
  
  /* Delete the specified file. Returns 0 on success, -1 on failure
   * Introduced in VFS API v1 */
  typedef int (RETRO_CALLCONV *retro_vfs_remove_t)(const char *path);
  
  /* Rename the specified file. Returns 0 on success, -1 on failure
   * Introduced in VFS API v1 */
  typedef int (RETRO_CALLCONV *retro_vfs_rename_t)(const char *old_path, const char *new_path);
  
  /* Stat the specified file. Retruns a bitmask of RETRO_VFS_STAT_* flags, none are set if path was not valid.
   * Additionally stores file size in given variable, unless NULL is given.
   * Introduced in VFS API v3 */
  typedef int (RETRO_CALLCONV *retro_vfs_stat_t)(const char *path, int32_t *size);
  
  /* Create the specified directory. Returns 0 on success, -1 on unknown failure, -2 if already exists.
   * Introduced in VFS API v3 */
  typedef int (RETRO_CALLCONV *retro_vfs_mkdir_t)(const char *dir);
  
  /* Open the specified directory for listing. Returns the opaque dir handle, or NULL for error.
   * Support for the include_hidden argument may vary depending on the platform.
   * Introduced in VFS API v3 */
  typedef struct retro_vfs_dir_handle *(RETRO_CALLCONV *retro_vfs_opendir_t)(const char *dir, bool include_hidden);
  
  /* Read the directory entry at the current position, and move the read pointer to the next position.
   * Returns true on success, false if already on the last entry.
   * Introduced in VFS API v3 */
  typedef bool (RETRO_CALLCONV *retro_vfs_readdir_t)(struct retro_vfs_dir_handle *dirstream);
  
  /* Get the name of the last entry read. Returns a string on success, or NULL for error.
   * The returned string pointer is valid until the next call to readdir or closedir.
   * Introduced in VFS API v3 */
  typedef const char *(RETRO_CALLCONV *retro_vfs_dirent_get_name_t)(struct retro_vfs_dir_handle *dirstream);
  
  /* Check if the last entry read was a directory. Returns true if it was, false otherwise (or on error).
   * Introduced in VFS API v3 */
  typedef bool (RETRO_CALLCONV *retro_vfs_dirent_is_dir_t)(struct retro_vfs_dir_handle *dirstream);
  
  /* Close the directory and release its resources. Must be called if opendir returns non-NULL. Returns 0 on success, -1 on failure.
   * Whether the call succeeds ot not, the handle passed as parameter becomes invalid and should no longer be used.
   * Introduced in VFS API v3 */
  typedef int (RETRO_CALLCONV *retro_vfs_closedir_t)(struct retro_vfs_dir_handle *dirstream);
  
  struct retro_vfs_interface
  {
     /* VFS API v1 */
  	retro_vfs_get_path_t get_path;
  	retro_vfs_open_t open;
  	retro_vfs_close_t close;
  	retro_vfs_size_t size;
  	retro_vfs_tell_t tell;
  	retro_vfs_seek_t seek;
  	retro_vfs_read_t read;
  	retro_vfs_write_t write;
  	retro_vfs_flush_t flush;
  	retro_vfs_remove_t remove;
  	retro_vfs_rename_t rename;
     /* VFS API v2 */
     retro_vfs_truncate_t truncate;
     /* VFS API v3 */
     retro_vfs_stat_t stat;
     retro_vfs_mkdir_t mkdir;
     retro_vfs_opendir_t opendir;
     retro_vfs_readdir_t readdir;
     retro_vfs_dirent_get_name_t dirent_get_name;
     retro_vfs_dirent_is_dir_t dirent_is_dir;
     retro_vfs_closedir_t closedir;
  };
  
  struct retro_vfs_interface_info
  {
     /* Set by core: should this be higher than the version the front end supports,
      * front end will return false in the RETRO_ENVIRONMENT_GET_VFS_INTERFACE call
      * Introduced in VFS API v1 */
     uint32_t required_interface_version;
  
     /* Frontend writes interface pointer here. The frontend also sets the actual
      * version, must be at least required_interface_version.
      * Introduced in VFS API v1 */
     struct retro_vfs_interface *iface;
  };
  
  enum retro_hw_render_interface_type
  {
  	RETRO_HW_RENDER_INTERFACE_VULKAN = 0,
  	RETRO_HW_RENDER_INTERFACE_D3D9   = 1,
  	RETRO_HW_RENDER_INTERFACE_D3D10  = 2,
  	RETRO_HW_RENDER_INTERFACE_D3D11  = 3,
  	RETRO_HW_RENDER_INTERFACE_D3D12  = 4,
     RETRO_HW_RENDER_INTERFACE_GSKIT_PS2  = 5,
     RETRO_HW_RENDER_INTERFACE_DUMMY  = INT_MAX
  };
  
  /* Base struct. All retro_hw_render_interface_* types
   * contain at least these fields. */
  struct retro_hw_render_interface
  {
     enum retro_hw_render_interface_type interface_type;
     unsigned interface_version;
  };
  
  typedef void (RETRO_CALLCONV *retro_set_led_state_t)(int led, int state);
  struct retro_led_interface
  {
      retro_set_led_state_t set_led_state;
  };
  
  /* Retrieves the current state of the MIDI input.
   * Returns true if it's enabled, false otherwise. */
  typedef bool (RETRO_CALLCONV *retro_midi_input_enabled_t)(void);
  
  /* Retrieves the current state of the MIDI output.
   * Returns true if it's enabled, false otherwise */
  typedef bool (RETRO_CALLCONV *retro_midi_output_enabled_t)(void);
  
  /* Reads next byte from the input stream.
   * Returns true if byte is read, false otherwise. */
  typedef bool (RETRO_CALLCONV *retro_midi_read_t)(uint8_t *byte);
  
  /* Writes byte to the output stream.
   * 'delta_time' is in microseconds and represent time elapsed since previous write.
   * Returns true if byte is written, false otherwise. */
  typedef bool (RETRO_CALLCONV *retro_midi_write_t)(uint8_t byte, uint32_t delta_time);
  
  /* Flushes previously written data.
   * Returns true if successful, false otherwise. */
  typedef bool (RETRO_CALLCONV *retro_midi_flush_t)(void);
  
  struct retro_midi_interface
  {
     retro_midi_input_enabled_t input_enabled;
     retro_midi_output_enabled_t output_enabled;
     retro_midi_read_t read;
     retro_midi_write_t write;
     retro_midi_flush_t flush;
  };
  
  enum retro_hw_render_context_negotiation_interface_type
  {
     RETRO_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE_VULKAN = 0,
     RETRO_HW_RENDER_CONTEXT_NEGOTIATION_INTERFACE_DUMMY = INT_MAX
  };
  
  /* Base struct. All retro_hw_render_context_negotiation_interface_* types
   * contain at least these fields. */
  struct retro_hw_render_context_negotiation_interface
  {
     enum retro_hw_render_context_negotiation_interface_type interface_type;
     unsigned interface_version;
  };
  
  /* Serialized state is incomplete in some way. Set if serialization is
   * usable in typical end-user cases but should not be relied upon to
   * implement frame-sensitive frontend features such as netplay or
   * rerecording. */
  #define RETRO_SERIALIZATION_QUIRK_INCOMPLETE (1 << 0)
  /* The core must spend some time initializing before serialization is
   * supported. retro_serialize() will initially fail; retro_unserialize()
   * and retro_serialize_size() may or may not work correctly either. */
  #define RETRO_SERIALIZATION_QUIRK_MUST_INITIALIZE (1 << 1)
  /* Serialization size may change within a session. */
  #define RETRO_SERIALIZATION_QUIRK_CORE_VARIABLE_SIZE (1 << 2)
  /* Set by the frontend to acknowledge that it supports variable-sized
   * states. */
  #define RETRO_SERIALIZATION_QUIRK_FRONT_VARIABLE_SIZE (1 << 3)
  /* Serialized state can only be loaded during the same session. */
  #define RETRO_SERIALIZATION_QUIRK_SINGLE_SESSION (1 << 4)
  /* Serialized state cannot be loaded on an architecture with a different
   * endianness from the one it was saved on. */
  #define RETRO_SERIALIZATION_QUIRK_ENDIAN_DEPENDENT (1 << 5)
  /* Serialized state cannot be loaded on a different platform from the one it
   * was saved on for reasons other than endianness, such as word size
   * dependence */
  #define RETRO_SERIALIZATION_QUIRK_PLATFORM_DEPENDENT (1 << 6)
  
  #define RETRO_MEMDESC_CONST      (1 << 0)   /* The frontend will never change this memory area once retro_load_game has returned. */
  #define RETRO_MEMDESC_BIGENDIAN  (1 << 1)   /* The memory area contains big endian data. Default is little endian. */
  #define RETRO_MEMDESC_SYSTEM_RAM (1 << 2)   /* The memory area is system RAM.  This is main RAM of the gaming system. */
  #define RETRO_MEMDESC_SAVE_RAM   (1 << 3)   /* The memory area is save RAM. This RAM is usually found on a game cartridge, backed up by a battery. */
  #define RETRO_MEMDESC_VIDEO_RAM  (1 << 4)   /* The memory area is video RAM (VRAM) */
  #define RETRO_MEMDESC_ALIGN_2    (1 << 16)  /* All memory access in this area is aligned to their own size, or 2, whichever is smaller. */
  #define RETRO_MEMDESC_ALIGN_4    (2 << 16)
  #define RETRO_MEMDESC_ALIGN_8    (3 << 16)
  #define RETRO_MEMDESC_MINSIZE_2  (1 << 24)  /* All memory in this region is accessed at least 2 bytes at the time. */
  #define RETRO_MEMDESC_MINSIZE_4  (2 << 24)
  #define RETRO_MEMDESC_MINSIZE_8  (3 << 24)
  struct retro_memory_descriptor
  {
     uint64_t flags;
  
     /* Pointer to the start of the relevant ROM or RAM chip.
      * It's strongly recommended to use 'offset' if possible, rather than
      * doing math on the pointer.
      *
      * If the same byte is mapped my multiple descriptors, their descriptors
      * must have the same pointer.
      * If 'start' does not point to the first byte in the pointer, put the
      * difference in 'offset' instead.
      *
      * May be NULL if there's nothing usable here (e.g. hardware registers and
      * open bus). No flags should be set if the pointer is NULL.
      * It's recommended to minimize the number of descriptors if possible,
      * but not mandatory. */
     void *ptr;
     size_t offset;
  
     /* This is the location in the emulated address space
      * where the mapping starts. */
     size_t start;
  
     /* Which bits must be same as in 'start' for this mapping to apply.
      * The first memory descriptor to claim a certain byte is the one
      * that applies.
      * A bit which is set in 'start' must also be set in this.
      * Can be zero, in which case each byte is assumed mapped exactly once.
      * In this case, 'len' must be a power of two. */
     size_t select;
  
     /* If this is nonzero, the set bits are assumed not connected to the
      * memory chip's address pins. */
     size_t disconnect;
  
     /* This one tells the size of the current memory area.
      * If, after start+disconnect are applied, the address is higher than
      * this, the highest bit of the address is cleared.
      *
      * If the address is still too high, the next highest bit is cleared.
      * Can be zero, in which case it's assumed to be infinite (as limited
      * by 'select' and 'disconnect'). */
     size_t len;
  
     /* To go from emulated address to physical address, the following
      * order applies:
      * Subtract 'start', pick off 'disconnect', apply 'len', add 'offset'. */
  
     /* The address space name must consist of only a-zA-Z0-9_-,
      * should be as short as feasible (maximum length is 8 plus the NUL),
      * and may not be any other address space plus one or more 0-9A-F
      * at the end.
      * However, multiple memory descriptors for the same address space is
      * allowed, and the address space name can be empty. NULL is treated
      * as empty.
      *
      * Address space names are case sensitive, but avoid lowercase if possible.
      * The same pointer may exist in multiple address spaces.
      *
      * Examples:
      * blank+blank - valid (multiple things may be mapped in the same namespace)
      * 'Sp'+'Sp' - valid (multiple things may be mapped in the same namespace)
      * 'A'+'B' - valid (neither is a prefix of each other)
      * 'S'+blank - valid ('S' is not in 0-9A-F)
      * 'a'+blank - valid ('a' is not in 0-9A-F)
      * 'a'+'A' - valid (neither is a prefix of each other)
      * 'AR'+blank - valid ('R' is not in 0-9A-F)
      * 'ARB'+blank - valid (the B can't be part of the address either, because
      *                      there is no namespace 'AR')
      * blank+'B' - not valid, because it's ambigous which address space B1234
      *             would refer to.
      * The length can't be used for that purpose; the frontend may want
      * to append arbitrary data to an address, without a separator. */
     const char *addrspace;
  
     /* TODO: When finalizing this one, add a description field, which should be
      * "WRAM" or something roughly equally long. */
  
     /* TODO: When finalizing this one, replace 'select' with 'limit', which tells
      * which bits can vary and still refer to the same address (limit = ~select).
      * TODO: limit? range? vary? something else? */
  
     /* TODO: When finalizing this one, if 'len' is above what 'select' (or
      * 'limit') allows, it's bankswitched. Bankswitched data must have both 'len'
      * and 'select' != 0, and the mappings don't tell how the system switches the
      * banks. */
  
     /* TODO: When finalizing this one, fix the 'len' bit removal order.
      * For len=0x1800, pointer 0x1C00 should go to 0x1400, not 0x0C00.
      * Algorithm: Take bits highest to lowest, but if it goes above len, clear
      * the most recent addition and continue on the next bit.
      * TODO: Can the above be optimized? Is "remove the lowest bit set in both
      * pointer and 'len'" equivalent? */
  
     /* TODO: Some emulators (MAME?) emulate big endian systems by only accessing
      * the emulated memory in 32-bit chunks, native endian. But that's nothing
      * compared to Darek Mihocka <http://www.emulators.com/docs/nx07_vm101.htm>
      * (section Emulation 103 - Nearly Free Byte Reversal) - he flips the ENTIRE
      * RAM backwards! I'll want to represent both of those, via some flags.
      *
      * I suspect MAME either didn't think of that idea, or don't want the #ifdef.
      * Not sure which, nor do I really care. */
  
     /* TODO: Some of those flags are unused and/or don't really make sense. Clean
      * them up. */
  };
  
  /* The frontend may use the largest value of 'start'+'select' in a
   * certain namespace to infer the size of the address space.
   *
   * If the address space is larger than that, a mapping with .ptr=NULL
   * should be at the end of the array, with .select set to all ones for
   * as long as the address space is big.
   *
   * Sample descriptors (minus .ptr, and RETRO_MEMFLAG_ on the flags):
   * SNES WRAM:
   * .start=0x7E0000, .len=0x20000
   * (Note that this must be mapped before the ROM in most cases; some of the
   * ROM mappers
   * try to claim $7E0000, or at least $7E8000.)
   * SNES SPC700 RAM:
   * .addrspace="S", .len=0x10000
   * SNES WRAM mirrors:
   * .flags=MIRROR, .start=0x000000, .select=0xC0E000, .len=0x2000
   * .flags=MIRROR, .start=0x800000, .select=0xC0E000, .len=0x2000
   * SNES WRAM mirrors, alternate equivalent descriptor:
   * .flags=MIRROR, .select=0x40E000, .disconnect=~0x1FFF
   * (Various similar constructions can be created by combining parts of
   * the above two.)
   * SNES LoROM (512KB, mirrored a couple of times):
   * .flags=CONST, .start=0x008000, .select=0x408000, .disconnect=0x8000, .len=512*1024
   * .flags=CONST, .start=0x400000, .select=0x400000, .disconnect=0x8000, .len=512*1024
   * SNES HiROM (4MB):
   * .flags=CONST,                 .start=0x400000, .select=0x400000, .len=4*1024*1024
   * .flags=CONST, .offset=0x8000, .start=0x008000, .select=0x408000, .len=4*1024*1024
   * SNES ExHiROM (8MB):
   * .flags=CONST, .offset=0,                  .start=0xC00000, .select=0xC00000, .len=4*1024*1024
   * .flags=CONST, .offset=4*1024*1024,        .start=0x400000, .select=0xC00000, .len=4*1024*1024
   * .flags=CONST, .offset=0x8000,             .start=0x808000, .select=0xC08000, .len=4*1024*1024
   * .flags=CONST, .offset=4*1024*1024+0x8000, .start=0x008000, .select=0xC08000, .len=4*1024*1024
   * Clarify the size of the address space:
   * .ptr=NULL, .select=0xFFFFFF
   * .len can be implied by .select in many of them, but was included for clarity.
   */
  
  struct retro_memory_map
  {
     const struct retro_memory_descriptor *descriptors;
     unsigned num_descriptors;
  };
  
  struct retro_controller_description
  {
     /* Human-readable description of the controller. Even if using a generic
      * input device type, this can be set to the particular device type the
      * core uses. */
     const char *desc;
  
     /* Device type passed to retro_set_controller_port_device(). If the device
      * type is a sub-class of a generic input device type, use the
      * RETRO_DEVICE_SUBCLASS macro to create an ID.
      *
      * E.g. RETRO_DEVICE_SUBCLASS(RETRO_DEVICE_JOYPAD, 1). */
     unsigned id;
  };
  
  struct retro_controller_info
  {
     const struct retro_controller_description *types;
     unsigned num_types;
  };
  
  struct retro_subsystem_memory_info
  {
     /* The extension associated with a memory type, e.g. "psram". */
     const char *extension;
  
     /* The memory type for retro_get_memory(). This should be at
      * least 0x100 to avoid conflict with standardized
      * libretro memory types. */
     unsigned type;
  };
  
  struct retro_subsystem_rom_info
  {
     /* Describes what the content is (SGB BIOS, GB ROM, etc). */
     const char *desc;
  
     /* Same definition as retro_get_system_info(). */
     const char *valid_extensions;
  
     /* Same definition as retro_get_system_info(). */
     bool need_fullpath;
  
     /* Same definition as retro_get_system_info(). */
     bool block_extract;
  
     /* This is set if the content is required to load a game.
      * If this is set to false, a zeroed-out retro_game_info can be passed. */
     bool required;
  
     /* Content can have multiple associated persistent
      * memory types (retro_get_memory()). */
     const struct retro_subsystem_memory_info *memory;
     unsigned num_memory;
  };
  
  struct retro_subsystem_info
  {
     /* Human-readable string of the subsystem type, e.g. "Super GameBoy" */
     const char *desc;
  
     /* A computer friendly short string identifier for the subsystem type.
      * This name must be [a-z].
      * E.g. if desc is "Super GameBoy", this can be "sgb".
      * This identifier can be used for command-line interfaces, etc.
      */
     const char *ident;
  
     /* Infos for each content file. The first entry is assumed to be the
      * "most significant" content for frontend purposes.
      * E.g. with Super GameBoy, the first content should be the GameBoy ROM,
      * as it is the most "significant" content to a user.
      * If a frontend creates new file paths based on the content used
      * (e.g. savestates), it should use the path for the first ROM to do so. */
     const struct retro_subsystem_rom_info *roms;
  
     /* Number of content files associated with a subsystem. */
     unsigned num_roms;
  
     /* The type passed to retro_load_game_special(). */
     unsigned id;
  };
  
  typedef void (RETRO_CALLCONV *retro_proc_address_t)(void);
  
  /* libretro API extension functions:
   * (None here so far).
   *
   * Get a symbol from a libretro core.
   * Cores should only return symbols which are actual
   * extensions to the libretro API.
   *
   * Frontends should not use this to obtain symbols to standard
   * libretro entry points (static linking or dlsym).
   *
   * The symbol name must be equal to the function name,
   * e.g. if void retro_foo(void); exists, the symbol must be called "retro_foo".
   * The returned function pointer must be cast to the corresponding type.
   */
  typedef retro_proc_address_t (RETRO_CALLCONV *retro_get_proc_address_t)(const char *sym);
  
  struct retro_get_proc_address_interface
  {
     retro_get_proc_address_t get_proc_address;
  };
  
  enum retro_log_level
  {
     RETRO_LOG_DEBUG = 0,
     RETRO_LOG_INFO,
     RETRO_LOG_WARN,
     RETRO_LOG_ERROR,
  
     RETRO_LOG_DUMMY = INT_MAX
  };
  
  /* Logging function. Takes log level argument as well. */
  typedef void (RETRO_CALLCONV *retro_log_printf_t)(enum retro_log_level level,
        const char *fmt, ...);
  
  struct retro_log_callback
  {
     retro_log_printf_t log;
  };
  
  /* Performance related functions */
  
  /* ID values for SIMD CPU features */
  #define RETRO_SIMD_SSE      (1 << 0)
  #define RETRO_SIMD_SSE2     (1 << 1)
  #define RETRO_SIMD_VMX      (1 << 2)
  #define RETRO_SIMD_VMX128   (1 << 3)
  #define RETRO_SIMD_AVX      (1 << 4)
  #define RETRO_SIMD_NEON     (1 << 5)
  #define RETRO_SIMD_SSE3     (1 << 6)
  #define RETRO_SIMD_SSSE3    (1 << 7)
  #define RETRO_SIMD_MMX      (1 << 8)
  #define RETRO_SIMD_MMXEXT   (1 << 9)
  #define RETRO_SIMD_SSE4     (1 << 10)
  #define RETRO_SIMD_SSE42    (1 << 11)
  #define RETRO_SIMD_AVX2     (1 << 12)
  #define RETRO_SIMD_VFPU     (1 << 13)
  #define RETRO_SIMD_PS       (1 << 14)
  #define RETRO_SIMD_AES      (1 << 15)
  #define RETRO_SIMD_VFPV3    (1 << 16)
  #define RETRO_SIMD_VFPV4    (1 << 17)
  #define RETRO_SIMD_POPCNT   (1 << 18)
  #define RETRO_SIMD_MOVBE    (1 << 19)
  #define RETRO_SIMD_CMOV     (1 << 20)
  #define RETRO_SIMD_ASIMD    (1 << 21)
  
  typedef uint64_t retro_perf_tick_t;
  typedef int64_t retro_time_t;
  
  struct retro_perf_counter
  {
     const char *ident;
     retro_perf_tick_t start;
     retro_perf_tick_t total;
     retro_perf_tick_t call_cnt;
  
     bool registered;
  };
  
  /* Returns current time in microseconds.
   * Tries to use the most accurate timer available.
   */
  typedef retro_time_t (RETRO_CALLCONV *retro_perf_get_time_usec_t)(void);
  
  /* A simple counter. Usually nanoseconds, but can also be CPU cycles.
   * Can be used directly if desired (when creating a more sophisticated
   * performance counter system).
   * */
  typedef retro_perf_tick_t (RETRO_CALLCONV *retro_perf_get_counter_t)(void);
  
  /* Returns a bit-mask of detected CPU features (RETRO_SIMD_*). */
  typedef uint64_t (RETRO_CALLCONV *retro_get_cpu_features_t)(void);
  
  /* Asks frontend to log and/or display the state of performance counters.
   * Performance counters can always be poked into manually as well.
   */
  typedef void (RETRO_CALLCONV *retro_perf_log_t)(void);
  
  /* Register a performance counter.
   * ident field must be set with a discrete value and other values in
   * retro_perf_counter must be 0.
   * Registering can be called multiple times. To avoid calling to
   * frontend redundantly, you can check registered field first. */
  typedef void (RETRO_CALLCONV *retro_perf_register_t)(struct retro_perf_counter *counter);
  
  /* Starts a registered counter. */
  typedef void (RETRO_CALLCONV *retro_perf_start_t)(struct retro_perf_counter *counter);
  
  /* Stops a registered counter. */
  typedef void (RETRO_CALLCONV *retro_perf_stop_t)(struct retro_perf_counter *counter);
  
  /* For convenience it can be useful to wrap register, start and stop in macros.
   * E.g.:
   * #ifdef LOG_PERFORMANCE
   * #define RETRO_PERFORMANCE_INIT(perf_cb, name) static struct retro_perf_counter name = {#name}; if (!name.registered) perf_cb.perf_register(&(name))
   * #define RETRO_PERFORMANCE_START(perf_cb, name) perf_cb.perf_start(&(name))
   * #define RETRO_PERFORMANCE_STOP(perf_cb, name) perf_cb.perf_stop(&(name))
   * #else
   * ... Blank macros ...
   * #endif
   *
   * These can then be used mid-functions around code snippets.
   *
   * extern struct retro_perf_callback perf_cb;  * Somewhere in the core.
   *
   * void do_some_heavy_work(void)
   * {
   *    RETRO_PERFORMANCE_INIT(cb, work_1;
   *    RETRO_PERFORMANCE_START(cb, work_1);
   *    heavy_work_1();
   *    RETRO_PERFORMANCE_STOP(cb, work_1);
   *
   *    RETRO_PERFORMANCE_INIT(cb, work_2);
   *    RETRO_PERFORMANCE_START(cb, work_2);
   *    heavy_work_2();
   *    RETRO_PERFORMANCE_STOP(cb, work_2);
   * }
   *
   * void retro_deinit(void)
   * {
   *    perf_cb.perf_log();  * Log all perf counters here for example.
   * }
   */
  
  struct retro_perf_callback
  {
     retro_perf_get_time_usec_t    get_time_usec;
     retro_get_cpu_features_t      get_cpu_features;
  
     retro_perf_get_counter_t      get_perf_counter;
     retro_perf_register_t         perf_register;
     retro_perf_start_t            perf_start;
     retro_perf_stop_t             perf_stop;
     retro_perf_log_t              perf_log;
  };
  
  /* FIXME: Document the sensor API and work out behavior.
   * It will be marked as experimental until then.
   */
  enum retro_sensor_action
  {
     RETRO_SENSOR_ACCELEROMETER_ENABLE = 0,
     RETRO_SENSOR_ACCELEROMETER_DISABLE,
     RETRO_SENSOR_GYROSCOPE_ENABLE,
     RETRO_SENSOR_GYROSCOPE_DISABLE,
     RETRO_SENSOR_ILLUMINANCE_ENABLE,
     RETRO_SENSOR_ILLUMINANCE_DISABLE,
  
     RETRO_SENSOR_DUMMY = INT_MAX
  };
  
  /* Id values for SENSOR types. */
  #define RETRO_SENSOR_ACCELEROMETER_X 0
  #define RETRO_SENSOR_ACCELEROMETER_Y 1
  #define RETRO_SENSOR_ACCELEROMETER_Z 2
  #define RETRO_SENSOR_GYROSCOPE_X 3
  #define RETRO_SENSOR_GYROSCOPE_Y 4
  #define RETRO_SENSOR_GYROSCOPE_Z 5
  #define RETRO_SENSOR_ILLUMINANCE 6
  
  typedef bool (RETRO_CALLCONV *retro_set_sensor_state_t)(unsigned port,
        enum retro_sensor_action action, unsigned rate);
  
  typedef float (RETRO_CALLCONV *retro_sensor_get_input_t)(unsigned port, unsigned id);
  
  struct retro_sensor_interface
  {
     retro_set_sensor_state_t set_sensor_state;
     retro_sensor_get_input_t get_sensor_input;
  };
  
  enum retro_camera_buffer
  {
     RETRO_CAMERA_BUFFER_OPENGL_TEXTURE = 0,
     RETRO_CAMERA_BUFFER_RAW_FRAMEBUFFER,
  
     RETRO_CAMERA_BUFFER_DUMMY = INT_MAX
  };
  
  /* Starts the camera driver. Can only be called in retro_run(). */
  typedef bool (RETRO_CALLCONV *retro_camera_start_t)(void);
  
  /* Stops the camera driver. Can only be called in retro_run(). */
  typedef void (RETRO_CALLCONV *retro_camera_stop_t)(void);
  
  /* Callback which signals when the camera driver is initialized
   * and/or deinitialized.
   * retro_camera_start_t can be called in initialized callback.
   */
  typedef void (RETRO_CALLCONV *retro_camera_lifetime_status_t)(void);
  
  /* A callback for raw framebuffer data. buffer points to an XRGB8888 buffer.
   * Width, height and pitch are similar to retro_video_refresh_t.
   * First pixel is top-left origin.
   */
  typedef void (RETRO_CALLCONV *retro_camera_frame_raw_framebuffer_t)(const uint32_t *buffer,
        unsigned width, unsigned height, size_t pitch);
  
  /* A callback for when OpenGL textures are used.
   *
   * texture_id is a texture owned by camera driver.
   * Its state or content should be considered immutable, except for things like
   * texture filtering and clamping.
   *
   * texture_target is the texture target for the GL texture.
   * These can include e.g. GL_TEXTURE_2D, GL_TEXTURE_RECTANGLE, and possibly
   * more depending on extensions.
   *
   * affine points to a packed 3x3 column-major matrix used to apply an affine
   * transform to texture coordinates. (affine_matrix * vec3(coord_x, coord_y, 1.0))
   * After transform, normalized texture coord (0, 0) should be bottom-left
   * and (1, 1) should be top-right (or (width, height) for RECTANGLE).
   *
   * GL-specific typedefs are avoided here to avoid relying on gl.h in
   * the API definition.
   */
  typedef void (RETRO_CALLCONV *retro_camera_frame_opengl_texture_t)(unsigned texture_id,
        unsigned texture_target, const float *affine);
  
  struct retro_camera_callback
  {
     /* Set by libretro core.
      * Example bitmask: caps = (1 << RETRO_CAMERA_BUFFER_OPENGL_TEXTURE) | (1 << RETRO_CAMERA_BUFFER_RAW_FRAMEBUFFER).
      */
     uint64_t caps;
  
     /* Desired resolution for camera. Is only used as a hint. */
     unsigned width;
     unsigned height;
  
     /* Set by frontend. */
     retro_camera_start_t start;
     retro_camera_stop_t stop;
  
     /* Set by libretro core if raw framebuffer callbacks will be used. */
     retro_camera_frame_raw_framebuffer_t frame_raw_framebuffer;
  
     /* Set by libretro core if OpenGL texture callbacks will be used. */
     retro_camera_frame_opengl_texture_t frame_opengl_texture;
  
     /* Set by libretro core. Called after camera driver is initialized and
      * ready to be started.
      * Can be NULL, in which this callback is not called.
      */
     retro_camera_lifetime_status_t initialized;
  
     /* Set by libretro core. Called right before camera driver is
      * deinitialized.
      * Can be NULL, in which this callback is not called.
      */
     retro_camera_lifetime_status_t deinitialized;
  };
  
  /* Sets the interval of time and/or distance at which to update/poll
   * location-based data.
   *
   * To ensure compatibility with all location-based implementations,
   * values for both interval_ms and interval_distance should be provided.
   *
   * interval_ms is the interval expressed in milliseconds.
   * interval_distance is the distance interval expressed in meters.
   */
  typedef void (RETRO_CALLCONV *retro_location_set_interval_t)(unsigned interval_ms,
        unsigned interval_distance);
  
  /* Start location services. The device will start listening for changes to the
   * current location at regular intervals (which are defined with
   * retro_location_set_interval_t). */
  typedef bool (RETRO_CALLCONV *retro_location_start_t)(void);
  
  /* Stop location services. The device will stop listening for changes
   * to the current location. */
  typedef void (RETRO_CALLCONV *retro_location_stop_t)(void);
  
  /* Get the position of the current location. Will set parameters to
   * 0 if no new  location update has happened since the last time. */
  typedef bool (RETRO_CALLCONV *retro_location_get_position_t)(double *lat, double *lon,
        double *horiz_accuracy, double *vert_accuracy);
  
  /* Callback which signals when the location driver is initialized
   * and/or deinitialized.
   * retro_location_start_t can be called in initialized callback.
   */
  typedef void (RETRO_CALLCONV *retro_location_lifetime_status_t)(void);
  
  struct retro_location_callback
  {
     retro_location_start_t         start;
     retro_location_stop_t          stop;
     retro_location_get_position_t  get_position;
     retro_location_set_interval_t  set_interval;
  
     retro_location_lifetime_status_t initialized;
     retro_location_lifetime_status_t deinitialized;
  };
  
  enum retro_rumble_effect
  {
     RETRO_RUMBLE_STRONG = 0,
     RETRO_RUMBLE_WEAK = 1,
  
     RETRO_RUMBLE_DUMMY = INT_MAX
  };
  
  /* Sets rumble state for joypad plugged in port 'port'.
   * Rumble effects are controlled independently,
   * and setting e.g. strong rumble does not override weak rumble.
   * Strength has a range of [0, 0xffff].
   *
   * Returns true if rumble state request was honored.
   * Calling this before first retro_run() is likely to return false. */
  typedef bool (RETRO_CALLCONV *retro_set_rumble_state_t)(unsigned port,
        enum retro_rumble_effect effect, uint16_t strength);
  
  struct retro_rumble_interface
  {
     retro_set_rumble_state_t set_rumble_state;
  };
  
  /* Notifies libretro that audio data should be written. */
  typedef void (RETRO_CALLCONV *retro_audio_callback_t)(void);
  
  /* True: Audio driver in frontend is active, and callback is
   * expected to be called regularily.
   * False: Audio driver in frontend is paused or inactive.
   * Audio callback will not be called until set_state has been
   * called with true.
   * Initial state is false (inactive).
   */
  typedef void (RETRO_CALLCONV *retro_audio_set_state_callback_t)(bool enabled);
  
  struct retro_audio_callback
  {
     retro_audio_callback_t callback;
     retro_audio_set_state_callback_t set_state;
  };
  
  /* Notifies a libretro core of time spent since last invocation
   * of retro_run() in microseconds.
   *
   * It will be called right before retro_run() every frame.
   * The frontend can tamper with timing to support cases like
   * fast-forward, slow-motion and framestepping.
   *
   * In those scenarios the reference frame time value will be used. */
  typedef int64_t retro_usec_t;
  typedef void (RETRO_CALLCONV *retro_frame_time_callback_t)(retro_usec_t usec);
  struct retro_frame_time_callback
  {
     retro_frame_time_callback_t callback;
     /* Represents the time of one frame. It is computed as
      * 1000000 / fps, but the implementation will resolve the
      * rounding to ensure that framestepping, etc is exact. */
     retro_usec_t reference;
  };
  
  /* Notifies a libretro core of the current occupancy
   * level of the frontend audio buffer.
   *
   * - active: 'true' if audio buffer is currently
   *           in use. Will be 'false' if audio is
   *           disabled in the frontend
   *
   * - occupancy: Given as a value in the range [0,100],
   *              corresponding to the occupancy percentage
   *              of the audio buffer
   *
   * - underrun_likely: 'true' if the frontend expects an
   *                    audio buffer underrun during the
   *                    next frame (indicates that a core
   *                    should attempt frame skipping)
   *
   * It will be called right before retro_run() every frame. */
  typedef void (RETRO_CALLCONV *retro_audio_buffer_status_callback_t)(
        bool active, unsigned occupancy, bool underrun_likely);
  struct retro_audio_buffer_status_callback
  {
     retro_audio_buffer_status_callback_t callback;
  };
  
  /* Pass this to retro_video_refresh_t if rendering to hardware.
   * Passing NULL to retro_video_refresh_t is still a frame dupe as normal.
   * */
  #define RETRO_HW_FRAME_BUFFER_VALID ((void*)-1)
  
  /* Invalidates the current HW context.
   * Any GL state is lost, and must not be deinitialized explicitly.
   * If explicit deinitialization is desired by the libretro core,
   * it should implement context_destroy callback.
   * If called, all GPU resources must be reinitialized.
   * Usually called when frontend reinits video driver.
   * Also called first time video driver is initialized,
   * allowing libretro core to initialize resources.
   */
  typedef void (RETRO_CALLCONV *retro_hw_context_reset_t)(void);
  
  /* Gets current framebuffer which is to be rendered to.
   * Could change every frame potentially.
   */
  typedef uintptr_t (RETRO_CALLCONV *retro_hw_get_current_framebuffer_t)(void);
  
  /* Get a symbol from HW context. */
  typedef retro_proc_address_t (RETRO_CALLCONV *retro_hw_get_proc_address_t)(const char *sym);
  
  enum retro_hw_context_type
  {
     RETRO_HW_CONTEXT_NONE             = 0,
     /* OpenGL 2.x. Driver can choose to use latest compatibility context. */
     RETRO_HW_CONTEXT_OPENGL           = 1,
     /* OpenGL ES 2.0. */
     RETRO_HW_CONTEXT_OPENGLES2        = 2,
     /* Modern desktop core GL context. Use version_major/
      * version_minor fields to set GL version. */
     RETRO_HW_CONTEXT_OPENGL_CORE      = 3,
     /* OpenGL ES 3.0 */
     RETRO_HW_CONTEXT_OPENGLES3        = 4,
     /* OpenGL ES 3.1+. Set version_major/version_minor. For GLES2 and GLES3,
      * use the corresponding enums directly. */
     RETRO_HW_CONTEXT_OPENGLES_VERSION = 5,
  
     /* Vulkan, see RETRO_ENVIRONMENT_GET_HW_RENDER_INTERFACE. */
     RETRO_HW_CONTEXT_VULKAN           = 6,
  
     /* Direct3D, set version_major to select the type of interface
      * returned by RETRO_ENVIRONMENT_GET_HW_RENDER_INTERFACE */
     RETRO_HW_CONTEXT_DIRECT3D         = 7,
  
     RETRO_HW_CONTEXT_DUMMY = INT_MAX
  };
  
  struct retro_hw_render_callback
  {
     /* Which API to use. Set by libretro core. */
     enum retro_hw_context_type context_type;
  
     /* Called when a context has been created or when it has been reset.
      * An OpenGL context is only valid after context_reset() has been called.
      *
      * When context_reset is called, OpenGL resources in the libretro
      * implementation are guaranteed to be invalid.
      *
      * It is possible that context_reset is called multiple times during an
      * application lifecycle.
      * If context_reset is called without any notification (context_destroy),
      * the OpenGL context was lost and resources should just be recreated
      * without any attempt to "free" old resources.
      */
     retro_hw_context_reset_t context_reset;
  
     /* Set by frontend.
      * TODO: This is rather obsolete. The frontend should not
      * be providing preallocated framebuffers. */
     retro_hw_get_current_framebuffer_t get_current_framebuffer;
  
     /* Set by frontend.
      * Can return all relevant functions, including glClear on Windows. */
     retro_hw_get_proc_address_t get_proc_address;
  
     /* Set if render buffers should have depth component attached.
      * TODO: Obsolete. */
     bool depth;
  
     /* Set if stencil buffers should be attached.
      * TODO: Obsolete. */
     bool stencil;
  
     /* If depth and stencil are true, a packed 24/8 buffer will be added.
      * Only attaching stencil is invalid and will be ignored. */
  
     /* Use conventional bottom-left origin convention. If false,
      * standard libretro top-left origin semantics are used.
      * TODO: Move to GL specific interface. */
     bool bottom_left_origin;
  
     /* Major version number for core GL context or GLES 3.1+. */
     unsigned version_major;
  
     /* Minor version number for core GL context or GLES 3.1+. */
     unsigned version_minor;
  
     /* If this is true, the frontend will go very far to avoid
      * resetting context in scenarios like toggling fullscreen, etc.
      * TODO: Obsolete? Maybe frontend should just always assume this ...
      */
     bool cache_context;
  
     /* The reset callback might still be called in extreme situations
      * such as if the context is lost beyond recovery.
      *
      * For optimal stability, set this to false, and allow context to be
      * reset at any time.
      */
  
     /* A callback to be called before the context is destroyed in a
      * controlled way by the frontend. */
     retro_hw_context_reset_t context_destroy;
  
     /* OpenGL resources can be deinitialized cleanly at this step.
      * context_destroy can be set to NULL, in which resources will
      * just be destroyed without any notification.
      *
      * Even when context_destroy is non-NULL, it is possible that
      * context_reset is called without any destroy notification.
      * This happens if context is lost by external factors (such as
      * notified by GL_ARB_robustness).
      *
      * In this case, the context is assumed to be already dead,
      * and the libretro implementation must not try to free any OpenGL
      * resources in the subsequent context_reset.
      */
  
     /* Creates a debug context. */
     bool debug_context;
  };
  
  /* Callback type passed in RETRO_ENVIRONMENT_SET_KEYBOARD_CALLBACK.
   * Called by the frontend in response to keyboard events.
   * down is set if the key is being pressed, or false if it is being released.
   * keycode is the RETROK value of the char.
   * character is the text character of the pressed key. (UTF-32).
   * key_modifiers is a set of RETROKMOD values or'ed together.
   *
   * The pressed/keycode state can be indepedent of the character.
   * It is also possible that multiple characters are generated from a
   * single keypress.
   * Keycode events should be treated separately from character events.
   * However, when possible, the frontend should try to synchronize these.
   * If only a character is posted, keycode should be RETROK_UNKNOWN.
   *
   * Similarily if only a keycode event is generated with no corresponding
   * character, character should be 0.
   */
  typedef void (RETRO_CALLCONV *retro_keyboard_event_t)(bool down, unsigned keycode,
        uint32_t character, uint16_t key_modifiers);
  
  struct retro_keyboard_callback
  {
     retro_keyboard_event_t callback;
  };
  
  /* Callbacks for RETRO_ENVIRONMENT_SET_DISK_CONTROL_INTERFACE &
   * RETRO_ENVIRONMENT_SET_DISK_CONTROL_EXT_INTERFACE.
   * Should be set for implementations which can swap out multiple disk
   * images in runtime.
   *
   * If the implementation can do this automatically, it should strive to do so.
   * However, there are cases where the user must manually do so.
   *
   * Overview: To swap a disk image, eject the disk image with
   * set_eject_state(true).
   * Set the disk index with set_image_index(index). Insert the disk again
   * with set_eject_state(false).
   */
  
  /* If ejected is true, "ejects" the virtual disk tray.
   * When ejected, the disk image index can be set.
   */
  typedef bool (RETRO_CALLCONV *retro_set_eject_state_t)(bool ejected);
  
  /* Gets current eject state. The initial state is 'not ejected'. */
  typedef bool (RETRO_CALLCONV *retro_get_eject_state_t)(void);
  
  /* Gets current disk index. First disk is index 0.
   * If return value is >= get_num_images(), no disk is currently inserted.
   */
  typedef unsigned (RETRO_CALLCONV *retro_get_image_index_t)(void);
  
  /* Sets image index. Can only be called when disk is ejected.
   * The implementation supports setting "no disk" by using an
   * index >= get_num_images().
   */
  typedef bool (RETRO_CALLCONV *retro_set_image_index_t)(unsigned index);
  
  /* Gets total number of images which are available to use. */
  typedef unsigned (RETRO_CALLCONV *retro_get_num_images_t)(void);
  
  struct retro_game_info;
  
  /* Replaces the disk image associated with index.
   * Arguments to pass in info have same requirements as retro_load_game().
   * Virtual disk tray must be ejected when calling this.
   *
   * Replacing a disk image with info = NULL will remove the disk image
   * from the internal list.
   * As a result, calls to get_image_index() can change.
   *
   * E.g. replace_image_index(1, NULL), and previous get_image_index()
   * returned 4 before.
   * Index 1 will be removed, and the new index is 3.
   */
  typedef bool (RETRO_CALLCONV *retro_replace_image_index_t)(unsigned index,
        const struct retro_game_info *info);
  
  /* Adds a new valid index (get_num_images()) to the internal disk list.
   * This will increment subsequent return values from get_num_images() by 1.
   * This image index cannot be used until a disk image has been set
   * with replace_image_index. */
  typedef bool (RETRO_CALLCONV *retro_add_image_index_t)(void);
  
  /* Sets initial image to insert in drive when calling
   * core_load_game().
   * Since we cannot pass the initial index when loading
   * content (this would require a major API change), this
   * is set by the frontend *before* calling the core's
   * retro_load_game()/retro_load_game_special() implementation.
   * A core should therefore cache the index/path values and handle
   * them inside retro_load_game()/retro_load_game_special().
   * - If 'index' is invalid (index >= get_num_images()), the
   *   core should ignore the set value and instead use 0
   * - 'path' is used purely for error checking - i.e. when
   *   content is loaded, the core should verify that the
   *   disk specified by 'index' has the specified file path.
   *   This is to guard against auto selecting the wrong image
   *   if (for example) the user should modify an existing M3U
   *   playlist. We have to let the core handle this because
   *   set_initial_image() must be called before loading content,
   *   i.e. the frontend cannot access image paths in advance
   *   and thus cannot perform the error check itself.
   *   If set path and content path do not match, the core should
   *   ignore the set 'index' value and instead use 0
   * Returns 'false' if index or 'path' are invalid, or core
   * does not support this functionality
   */
  typedef bool (RETRO_CALLCONV *retro_set_initial_image_t)(unsigned index, const char *path);
  
  /* Fetches the path of the specified disk image file.
   * Returns 'false' if index is invalid (index >= get_num_images())
   * or path is otherwise unavailable.
   */
  typedef bool (RETRO_CALLCONV *retro_get_image_path_t)(unsigned index, char *path, size_t len);
  
  /* Fetches a core-provided 'label' for the specified disk
   * image file. In the simplest case this may be a file name
   * (without extension), but for cores with more complex
   * content requirements information may be provided to
   * facilitate user disk swapping - for example, a core
   * running floppy-disk-based content may uniquely label
   * save disks, data disks, level disks, etc. with names
   * corresponding to in-game disk change prompts (so the
   * frontend can provide better user guidance than a 'dumb'
   * disk index value).
   * Returns 'false' if index is invalid (index >= get_num_images())
   * or label is otherwise unavailable.
   */
  typedef bool (RETRO_CALLCONV *retro_get_image_label_t)(unsigned index, char *label, size_t len);
  
  struct retro_disk_control_callback
  {
     retro_set_eject_state_t set_eject_state;
     retro_get_eject_state_t get_eject_state;
  
     retro_get_image_index_t get_image_index;
     retro_set_image_index_t set_image_index;
     retro_get_num_images_t  get_num_images;
  
     retro_replace_image_index_t replace_image_index;
     retro_add_image_index_t add_image_index;
  };
  
  struct retro_disk_control_ext_callback
  {
     retro_set_eject_state_t set_eject_state;
     retro_get_eject_state_t get_eject_state;
  
     retro_get_image_index_t get_image_index;
     retro_set_image_index_t set_image_index;
     retro_get_num_images_t  get_num_images;
  
     retro_replace_image_index_t replace_image_index;
     retro_add_image_index_t add_image_index;
  
     /* NOTE: Frontend will only attempt to record/restore
      * last used disk index if both set_initial_image()
      * and get_image_path() are implemented */
     retro_set_initial_image_t set_initial_image; /* Optional - may be NULL */
  
     retro_get_image_path_t get_image_path;       /* Optional - may be NULL */
     retro_get_image_label_t get_image_label;     /* Optional - may be NULL */
  };
  
  enum retro_pixel_format
  {
     /* 0RGB1555, native endian.
      * 0 bit must be set to 0.
      * This pixel format is default for compatibility concerns only.
      * If a 15/16-bit pixel format is desired, consider using RGB565. */
     RETRO_PIXEL_FORMAT_0RGB1555 = 0,
  
     /* XRGB8888, native endian.
      * X bits are ignored. */
     RETRO_PIXEL_FORMAT_XRGB8888 = 1,
  
     /* RGB565, native endian.
      * This pixel format is the recommended format to use if a 15/16-bit
      * format is desired as it is the pixel format that is typically
      * available on a wide range of low-power devices.
      *
      * It is also natively supported in APIs like OpenGL ES. */
     RETRO_PIXEL_FORMAT_RGB565   = 2,
  
     /* Ensure sizeof() == sizeof(int). */
     RETRO_PIXEL_FORMAT_UNKNOWN  = INT_MAX
  };
  
  struct retro_message
  {
     const char *msg;        /* Message to be displayed. */
     unsigned    frames;     /* Duration in frames of message. */
  };
  
  enum retro_message_target
  {
     RETRO_MESSAGE_TARGET_ALL = 0,
     RETRO_MESSAGE_TARGET_OSD,
     RETRO_MESSAGE_TARGET_LOG
  };
  
  enum retro_message_type
  {
     RETRO_MESSAGE_TYPE_NOTIFICATION = 0,
     RETRO_MESSAGE_TYPE_NOTIFICATION_ALT,
     RETRO_MESSAGE_TYPE_STATUS,
     RETRO_MESSAGE_TYPE_PROGRESS
  };
  
  struct retro_message_ext
  {
     /* Message string to be displayed/logged */
     const char *msg;
     /* Duration (in ms) of message when targeting the OSD */
     unsigned duration;
     /* Message priority when targeting the OSD
      * > When multiple concurrent messages are sent to
      *   the frontend and the frontend does not have the
      *   capacity to display them all, messages with the
      *   *highest* priority value should be shown
      * > There is no upper limit to a message priority
      *   value (within the bounds of the unsigned data type)
      * > In the reference frontend (RetroArch), the same
      *   priority values are used for frontend-generated
      *   notifications, which are typically assigned values
      *   between 0 and 3 depending upon importance */
     unsigned priority;
     /* Message logging level (info, warn, error, etc.) */
     enum retro_log_level level;
     /* Message destination: OSD, logging interface or both */
     enum retro_message_target target;
     /* Message 'type' when targeting the OSD
      * > RETRO_MESSAGE_TYPE_NOTIFICATION: Specifies that a
      *   message should be handled in identical fashion to
      *   a standard frontend-generated notification
      * > RETRO_MESSAGE_TYPE_NOTIFICATION_ALT: Specifies that
      *   message is a notification that requires user attention
      *   or action, but that it should be displayed in a manner
      *   that differs from standard frontend-generated notifications.
      *   This would typically correspond to messages that should be
      *   displayed immediately (independently from any internal
      *   frontend message queue), and/or which should be visually
      *   distinguishable from frontend-generated notifications.
      *   For example, a core may wish to inform the user of
      *   information related to a disk-change event. It is
      *   expected that the frontend itself may provide a
      *   notification in this case; if the core sends a
      *   message of type RETRO_MESSAGE_TYPE_NOTIFICATION, an
      *   uncomfortable 'double-notification' may occur. A message
      *   of RETRO_MESSAGE_TYPE_NOTIFICATION_ALT should therefore
      *   be presented such that visual conflict with regular
      *   notifications does not occur
      * > RETRO_MESSAGE_TYPE_STATUS: Indicates that message
      *   is not a standard notification. This typically
      *   corresponds to 'status' indicators, such as a core's
      *   internal FPS, which are intended to be displayed
      *   either permanently while a core is running, or in
      *   a manner that does not suggest user attention or action
      *   is required. 'Status' type messages should therefore be
      *   displayed in a different on-screen location and in a manner
      *   easily distinguishable from both standard frontend-generated
      *   notifications and messages of type RETRO_MESSAGE_TYPE_NOTIFICATION_ALT
      * > RETRO_MESSAGE_TYPE_PROGRESS: Indicates that message reports
      *   the progress of an internal core task. For example, in cases
      *   where a core itself handles the loading of content from a file,
      *   this may correspond to the percentage of the file that has been
      *   read. Alternatively, an audio/video playback core may use a
      *   message of type RETRO_MESSAGE_TYPE_PROGRESS to display the current
      *   playback position as a percentage of the runtime. 'Progress' type
      *   messages should therefore be displayed as a literal progress bar,
      *   where:
      *   - 'retro_message_ext.msg' is the progress bar title/label
      *   - 'retro_message_ext.progress' determines the length of
      *     the progress bar
      * NOTE: Message type is a *hint*, and may be ignored
      * by the frontend. If a frontend lacks support for
      * displaying messages via alternate means than standard
      * frontend-generated notifications, it will treat *all*
      * messages as having the type RETRO_MESSAGE_TYPE_NOTIFICATION */
     enum retro_message_type type;
     /* Task progress when targeting the OSD and message is
      * of type RETRO_MESSAGE_TYPE_PROGRESS
      * > -1:    Unmetered/indeterminate
      * > 0-100: Current progress percentage
      * NOTE: Since message type is a hint, a frontend may ignore
      * progress values. Where relevant, a core should therefore
      * include progress percentage within the message string,
      * such that the message intent remains clear when displayed
      * as a standard frontend-generated notification */
     int8_t progress;
  };
  
  /* Describes how the libretro implementation maps a libretro input bind
   * to its internal input system through a human readable string.
   * This string can be used to better let a user configure input. */
  struct retro_input_descriptor
  {
     /* Associates given parameters with a description. */
     unsigned port;
     unsigned device;
     unsigned index;
     unsigned id;
  
     /* Human readable description for parameters.
      * The pointer must remain valid until
      * retro_unload_game() is called. */
     const char *description;
  };
  
  struct retro_system_info
  {
     /* All pointers are owned by libretro implementation, and pointers must
      * remain valid until it is unloaded. */
  
     const char *library_name;      /* Descriptive name of library. Should not
                                     * contain any version numbers, etc. */
     const char *library_version;   /* Descriptive version of core. */
  
     const char *valid_extensions;  /* A string listing probably content
                                     * extensions the core will be able to
                                     * load, separated with pipe.
                                     * I.e. "bin|rom|iso".
                                     * Typically used for a GUI to filter
                                     * out extensions. */
  
     /* Libretro cores that need to have direct access to their content
      * files, including cores which use the path of the content files to
      * determine the paths of other files, should set need_fullpath to true.
      *
      * Cores should strive for setting need_fullpath to false,
      * as it allows the frontend to perform patching, etc.
      *
      * If need_fullpath is true and retro_load_game() is called:
      *    - retro_game_info::path is guaranteed to have a valid path
      *    - retro_game_info::data and retro_game_info::size are invalid
      *
      * If need_fullpath is false and retro_load_game() is called:
      *    - retro_game_info::path may be NULL
      *    - retro_game_info::data and retro_game_info::size are guaranteed
      *      to be valid
      *
      * See also:
      *    - RETRO_ENVIRONMENT_GET_SYSTEM_DIRECTORY
      *    - RETRO_ENVIRONMENT_GET_SAVE_DIRECTORY
      */
     bool        need_fullpath;
  
     /* If true, the frontend is not allowed to extract any archives before
      * loading the real content.
      * Necessary for certain libretro implementations that load games
      * from zipped archives. */
     bool        block_extract;
  };
  
  /* Defines overrides which modify frontend handling of
   * specific content file types.
   * An array of retro_system_content_info_override is
   * passed to RETRO_ENVIRONMENT_SET_CONTENT_INFO_OVERRIDE
   * NOTE: In the following descriptions, references to
   *       retro_load_game() may be replaced with
   *       retro_load_game_special() */
  struct retro_system_content_info_override
  {
     /* A list of file extensions for which the override
      * should apply, delimited by a 'pipe' character
      * (e.g. "md|sms|gg")
      * Permitted file extensions are limited to those
      * included in retro_system_info::valid_extensions
      * and/or retro_subsystem_rom_info::valid_extensions */
     const char *extensions;
  
     /* Overrides the need_fullpath value set in
      * retro_system_info and/or retro_subsystem_rom_info.
      * To reiterate:
      *
      * If need_fullpath is true and retro_load_game() is called:
      *    - retro_game_info::path is guaranteed to contain a valid
      *      path to an existent file
      *    - retro_game_info::data and retro_game_info::size are invalid
      *
      * If need_fullpath is false and retro_load_game() is called:
      *    - retro_game_info::path may be NULL
      *    - retro_game_info::data and retro_game_info::size are guaranteed
      *      to be valid
      *
      * In addition:
      *
      * If need_fullpath is true and retro_load_game() is called:
      *    - retro_game_info_ext::full_path is guaranteed to contain a valid
      *      path to an existent file
      *    - retro_game_info_ext::archive_path may be NULL
      *    - retro_game_info_ext::archive_file may be NULL
      *    - retro_game_info_ext::dir is guaranteed to contain a valid path
      *      to the directory in which the content file exists
      *    - retro_game_info_ext::name is guaranteed to contain the
      *      basename of the content file, without extension
      *    - retro_game_info_ext::ext is guaranteed to contain the
      *      extension of the content file in lower case format
      *    - retro_game_info_ext::data and retro_game_info_ext::size
      *      are invalid
      *
      * If need_fullpath is false and retro_load_game() is called:
      *    - If retro_game_info_ext::file_in_archive is false:
      *       - retro_game_info_ext::full_path is guaranteed to contain
      *         a valid path to an existent file
      *       - retro_game_info_ext::archive_path may be NULL
      *       - retro_game_info_ext::archive_file may be NULL
      *       - retro_game_info_ext::dir is guaranteed to contain a
      *         valid path to the directory in which the content file exists
      *       - retro_game_info_ext::name is guaranteed to contain the
      *         basename of the content file, without extension
      *       - retro_game_info_ext::ext is guaranteed to contain the
      *         extension of the content file in lower case format
      *    - If retro_game_info_ext::file_in_archive is true:
      *       - retro_game_info_ext::full_path may be NULL
      *       - retro_game_info_ext::archive_path is guaranteed to
      *         contain a valid path to an existent compressed file
      *         inside which the content file is located
      *       - retro_game_info_ext::archive_file is guaranteed to
      *         contain a valid path to an existent content file
      *         inside the compressed file referred to by
      *         retro_game_info_ext::archive_path
      *            e.g. for a compressed file '/path/to/foo.zip'
      *            containing 'bar.sfc'
      *             > retro_game_info_ext::archive_path will be '/path/to/foo.zip'
      *             > retro_game_info_ext::archive_file will be 'bar.sfc'
      *       - retro_game_info_ext::dir is guaranteed to contain a
      *         valid path to the directory in which the compressed file
      *         (containing the content file) exists
      *       - retro_game_info_ext::name is guaranteed to contain
      *         EITHER
      *         1) the basename of the compressed file (containing
      *            the content file), without extension
      *         OR
      *         2) the basename of the content file inside the
      *            compressed file, without extension
      *         In either case, a core should consider 'name' to
      *         be the canonical name/ID of the the content file
      *       - retro_game_info_ext::ext is guaranteed to contain the
      *         extension of the content file inside the compressed file,
      *         in lower case format
      *    - retro_game_info_ext::data and retro_game_info_ext::size are
      *      guaranteed to be valid */
     bool need_fullpath;
  
     /* If need_fullpath is false, specifies whether the content
      * data buffer available in retro_load_game() is 'persistent'
      *
      * If persistent_data is false and retro_load_game() is called:
      *    - retro_game_info::data and retro_game_info::size
      *      are valid only until retro_load_game() returns
      *    - retro_game_info_ext::data and retro_game_info_ext::size
      *      are valid only until retro_load_game() returns
      *
      * If persistent_data is true and retro_load_game() is called:
      *    - retro_game_info::data and retro_game_info::size
      *      are valid until retro_deinit() returns
      *    - retro_game_info_ext::data and retro_game_info_ext::size
      *      are valid until retro_deinit() returns */
     bool persistent_data;
  };
  
  /* Similar to retro_game_info, but provides extended
   * information about the source content file and
   * game memory buffer status.
   * And array of retro_game_info_ext is returned by
   * RETRO_ENVIRONMENT_GET_GAME_INFO_EXT
   * NOTE: In the following descriptions, references to
   *       retro_load_game() may be replaced with
   *       retro_load_game_special() */
  struct retro_game_info_ext
  {
     /* - If file_in_archive is false, contains a valid
      *   path to an existent content file (UTF-8 encoded)
      * - If file_in_archive is true, may be NULL */
     const char *full_path;
  
     /* - If file_in_archive is false, may be NULL
      * - If file_in_archive is true, contains a valid path
      *   to an existent compressed file inside which the
      *   content file is located (UTF-8 encoded) */
     const char *archive_path;
  
     /* - If file_in_archive is false, may be NULL
      * - If file_in_archive is true, contain a valid path
      *   to an existent content file inside the compressed
      *   file referred to by archive_path (UTF-8 encoded)
      *      e.g. for a compressed file '/path/to/foo.zip'
      *      containing 'bar.sfc'
      *      > archive_path will be '/path/to/foo.zip'
      *      > archive_file will be 'bar.sfc' */
     const char *archive_file;
  
     /* - If file_in_archive is false, contains a valid path
      *   to the directory in which the content file exists
      *   (UTF-8 encoded)
      * - If file_in_archive is true, contains a valid path
      *   to the directory in which the compressed file
      *   (containing the content file) exists (UTF-8 encoded) */
     const char *dir;
  
     /* Contains the canonical name/ID of the content file
      * (UTF-8 encoded). Intended for use when identifying
      * 'complementary' content named after the loaded file -
      * i.e. companion data of a different format (a CD image
      * required by a ROM), texture packs, internally handled
      * save files, etc.
      * - If file_in_archive is false, contains the basename
      *   of the content file, without extension
      * - If file_in_archive is true, then string is
      *   implementation specific. A frontend may choose to
      *   set a name value of:
      *   EITHER
      *   1) the basename of the compressed file (containing
      *      the content file), without extension
      *   OR
      *   2) the basename of the content file inside the
      *      compressed file, without extension
      *   RetroArch sets the 'name' value according to (1).
      *   A frontend that supports routine loading of
      *   content from archives containing multiple unrelated
      *   content files may set the 'name' value according
      *   to (2). */
     const char *name;
  
     /* - If file_in_archive is false, contains the extension
      *   of the content file in lower case format
      * - If file_in_archive is true, contains the extension
      *   of the content file inside the compressed file,
      *   in lower case format */
     const char *ext;
  
     /* String of implementation specific meta-data. */
     const char *meta;
  
     /* Memory buffer of loaded game content. Will be NULL:
      * IF
      * - retro_system_info::need_fullpath is true and
      *   retro_system_content_info_override::need_fullpath
      *   is unset
      * OR
      * - retro_system_content_info_override::need_fullpath
      *   is true */
     const void *data;
  
     /* Size of game content memory buffer, in bytes */
     size_t size;
  
     /* True if loaded content file is inside a compressed
      * archive */
     bool file_in_archive;
  
     /* - If data is NULL, value is unset/ignored
      * - If data is non-NULL:
      *   - If persistent_data is false, data and size are
      *     valid only until retro_load_game() returns
      *   - If persistent_data is true, data and size are
      *     are valid until retro_deinit() returns */
     bool persistent_data;
  };
  
  struct retro_game_geometry
  {
     unsigned base_width;    /* Nominal video width of game. */
     unsigned base_height;   /* Nominal video height of game. */
     unsigned max_width;     /* Maximum possible width of game. */
     unsigned max_height;    /* Maximum possible height of game. */
  
     float    aspect_ratio;  /* Nominal aspect ratio of game. If
                              * aspect_ratio is <= 0.0, an aspect ratio
                              * of base_width / base_height is assumed.
                              * A frontend could override this setting,
                              * if desired. */
  };
  
  struct retro_system_timing
  {
     double fps;             /* FPS of video content. */
     double sample_rate;     /* Sampling rate of audio. */
  };
  
  struct retro_system_av_info
  {
     struct retro_game_geometry geometry;
     struct retro_system_timing timing;
  };
  
  struct retro_variable
  {
     /* Variable to query in RETRO_ENVIRONMENT_GET_VARIABLE.
      * If NULL, obtains the complete environment string if more
      * complex parsing is necessary.
      * The environment string is formatted as key-value pairs
      * delimited by semicolons as so:
      * "key1=value1;key2=value2;..."
      */
     const char *key;
  
     /* Value to be obtained. If key does not exist, it is set to NULL. */
     const char *value;
  };
  
  struct retro_core_option_display
  {
     /* Variable to configure in RETRO_ENVIRONMENT_SET_CORE_OPTIONS_DISPLAY */
     const char *key;
  
     /* Specifies whether variable should be displayed
      * when presenting core options to the user */
     bool visible;
  };
  
  /* Maximum number of values permitted for a core option
   * > Note: We have to set a maximum value due the limitations
   *   of the C language - i.e. it is not possible to create an
   *   array of structs each containing a variable sized array,
   *   so the retro_core_option_definition values array must
   *   have a fixed size. The size limit of 128 is a balancing
   *   act - it needs to be large enough to support all 'sane'
   *   core options, but setting it too large may impact low memory
   *   platforms. In practise, if a core option has more than
   *   128 values then the implementation is likely flawed.
   *   To quote the above API reference:
   *      "The number of possible options should be very limited
   *       i.e. it should be feasible to cycle through options
   *       without a keyboard."
   */
  #define RETRO_NUM_CORE_OPTION_VALUES_MAX 128
  
  struct retro_core_option_value
  {
     /* Expected option value */
     const char *value;
  
     /* Human-readable value label. If NULL, value itself
      * will be displayed by the frontend */
     const char *label;
  };
  
  struct retro_core_option_definition
  {
     /* Variable to query in RETRO_ENVIRONMENT_GET_VARIABLE. */
     const char *key;
  
     /* Human-readable core option description (used as menu label) */
     const char *desc;
  
     /* Human-readable core option information (used as menu sublabel) */
     const char *info;
  
     /* Array of retro_core_option_value structs, terminated by NULL */
     struct retro_core_option_value values[RETRO_NUM_CORE_OPTION_VALUES_MAX];
  
     /* Default core option value. Must match one of the values
      * in the retro_core_option_value array, otherwise will be
      * ignored */
     const char *default_value;
  };
  
  #ifdef __PS3__
  #undef local
  #endif
  
  struct retro_core_options_intl
  {
     /* Pointer to an array of retro_core_option_definition structs
      * - US English implementation
      * - Must point to a valid array */
     struct retro_core_option_definition *us;
  
     /* Pointer to an array of retro_core_option_definition structs
      * - Implementation for current frontend language
      * - May be NULL */
     struct retro_core_option_definition *local;
  };
  
  struct retro_core_option_v2_category
  {
     /* Variable uniquely identifying the
      * option category. Valid key characters
      * are [a-z, A-Z, 0-9, _, -] */
     const char *key;
  
     /* Human-readable category description
      * > Used as category menu label when
      *   frontend has core option category
      *   support */
     const char *desc;
  
     /* Human-readable category information
      * > Used as category menu sublabel when
      *   frontend has core option category
      *   support
      * > Optional (may be NULL or an empty
      *   string) */
     const char *info;
  };
  
  struct retro_core_option_v2_definition
  {
     /* Variable to query in RETRO_ENVIRONMENT_GET_VARIABLE.
      * Valid key characters are [a-z, A-Z, 0-9, _, -] */
     const char *key;
  
     /* Human-readable core option description
      * > Used as menu label when frontend does
      *   not have core option category support
      *   e.g. "Video > Aspect Ratio" */
     const char *desc;
  
     /* Human-readable core option description
      * > Used as menu label when frontend has
      *   core option category support
      *   e.g. "Aspect Ratio", where associated
      *   retro_core_option_v2_category::desc
      *   is "Video"
      * > If empty or NULL, the string specified by
      *   desc will be used as the menu label
      * > Will be ignored (and may be set to NULL)
      *   if category_key is empty or NULL */
     const char *desc_categorized;
  
     /* Human-readable core option information
      * > Used as menu sublabel */
     const char *info;
  
     /* Human-readable core option information
      * > Used as menu sublabel when frontend
      *   has core option category support
      *   (e.g. may be required when info text
      *   references an option by name/desc,
      *   and the desc/desc_categorized text
      *   for that option differ)
      * > If empty or NULL, the string specified by
      *   info will be used as the menu sublabel
      * > Will be ignored (and may be set to NULL)
      *   if category_key is empty or NULL */
     const char *info_categorized;
  
     /* Variable specifying category (e.g. "video",
      * "audio") that will be assigned to the option
      * if frontend has core option category support.
      * > Categorized options will be displayed in a
      *   subsection/submenu of the frontend core
      *   option interface
      * > Specified string must match one of the
      *   retro_core_option_v2_category::key values
      *   in the associated retro_core_option_v2_category
      *   array; If no match is not found, specified
      *   string will be considered as NULL
      * > If specified string is empty or NULL, option will
      *   have no category and will be shown at the top
      *   level of the frontend core option interface */
     const char *category_key;
  
     /* Array of retro_core_option_value structs, terminated by NULL */
     struct retro_core_option_value values[RETRO_NUM_CORE_OPTION_VALUES_MAX];
  
     /* Default core option value. Must match one of the values
      * in the retro_core_option_value array, otherwise will be
      * ignored */
     const char *default_value;
  };
  
  struct retro_core_options_v2
  {
     /* Array of retro_core_option_v2_category structs,
      * terminated by NULL
      * > If NULL, all entries in definitions array
      *   will have no category and will be shown at
      *   the top level of the frontend core option
      *   interface
      * > Will be ignored if frontend does not have
      *   core option category support */
     struct retro_core_option_v2_category *categories;
  
     /* Array of retro_core_option_v2_definition structs,
      * terminated by NULL */
     struct retro_core_option_v2_definition *definitions;
  };
  
  struct retro_core_options_v2_intl
  {
     /* Pointer to a retro_core_options_v2 struct
      * > US English implementation
      * > Must point to a valid struct */
     struct retro_core_options_v2 *us;
  
     /* Pointer to a retro_core_options_v2 struct
      * - Implementation for current frontend language
      * - May be NULL */
     struct retro_core_options_v2 *local;
  };
  
  /* Used by the frontend to monitor changes in core option
   * visibility. May be called each time any core option
   * value is set via the frontend.
   * - On each invocation, the core must update the visibility
   *   of any dynamically hidden options using the
   *   RETRO_ENVIRONMENT_SET_CORE_OPTIONS_DISPLAY environment
   *   callback.
   * - On the first invocation, returns 'true' if the visibility
   *   of any core option has changed since the last call of
   *   retro_load_game() or retro_load_game_special().
   * - On each subsequent invocation, returns 'true' if the
   *   visibility of any core option has changed since the last
   *   time the function was called. */
  typedef bool (RETRO_CALLCONV *retro_core_options_update_display_callback_t)(void);
  struct retro_core_options_update_display_callback
  {
     retro_core_options_update_display_callback_t callback;
  };
  
  struct retro_game_info
  {
     const char *path;       /* Path to game, UTF-8 encoded.
                              * Sometimes used as a reference for building other paths.
                              * May be NULL if game was loaded from stdin or similar,
                              * but in this case some cores will be unable to load `data`.
                              * So, it is preferable to fabricate something here instead
                              * of passing NULL, which will help more cores to succeed.
                              * retro_system_info::need_fullpath requires
                              * that this path is valid. */
     const void *data;       /* Memory buffer of loaded game. Will be NULL
                              * if need_fullpath was set. */
     size_t      size;       /* Size of memory buffer. */
     const char *meta;       /* String of implementation specific meta-data. */
  };
  
  #define RETRO_MEMORY_ACCESS_WRITE (1 << 0)
     /* The core will write to the buffer provided by retro_framebuffer::data. */
  #define RETRO_MEMORY_ACCESS_READ (1 << 1)
     /* The core will read from retro_framebuffer::data. */
  #define RETRO_MEMORY_TYPE_CACHED (1 << 0)
     /* The memory in data is cached.
      * If not cached, random writes and/or reading from the buffer is expected to be very slow. */
  struct retro_framebuffer
  {
     void *data;                      /* The framebuffer which the core can render into.
                                         Set by frontend in GET_CURRENT_SOFTWARE_FRAMEBUFFER.
                                         The initial contents of data are unspecified. */
     unsigned width;                  /* The framebuffer width used by the core. Set by core. */
     unsigned height;                 /* The framebuffer height used by the core. Set by core. */
     size_t pitch;                    /* The number of bytes between the beginning of a scanline,
                                         and beginning of the next scanline.
                                         Set by frontend in GET_CURRENT_SOFTWARE_FRAMEBUFFER. */
     enum retro_pixel_format format;  /* The pixel format the core must use to render into data.
                                         This format could differ from the format used in
                                         SET_PIXEL_FORMAT.
                                         Set by frontend in GET_CURRENT_SOFTWARE_FRAMEBUFFER. */
  
     unsigned access_flags;           /* How the core will access the memory in the framebuffer.
                                         RETRO_MEMORY_ACCESS_* flags.
                                         Set by core. */
     unsigned memory_flags;           /* Flags telling core how the memory has been mapped.
                                         RETRO_MEMORY_TYPE_* flags.
                                         Set by frontend in GET_CURRENT_SOFTWARE_FRAMEBUFFER. */
  };
  
  /* Used by a libretro core to override the current
   * fastforwarding mode of the frontend */
  struct retro_fastforwarding_override
  {
     /* Specifies the runtime speed multiplier that
      * will be applied when 'fastforward' is true.
      * For example, a value of 5.0 when running 60 FPS
      * content will cap the fast-forward rate at 300 FPS.
      * Note that the target multiplier may not be achieved
      * if the host hardware has insufficient processing
      * power.
      * Setting a value of 0.0 (or greater than 0.0 but
      * less than 1.0) will result in an uncapped
      * fast-forward rate (limited only by hardware
      * capacity).
      * If the value is negative, it will be ignored
      * (i.e. the frontend will use a runtime speed
      * multiplier of its own choosing) */
     float ratio;
  
     /* If true, fastforwarding mode will be enabled.
      * If false, fastforwarding mode will be disabled. */
     bool fastforward;
  
     /* If true, and if supported by the frontend, an
      * on-screen notification will be displayed while
      * 'fastforward' is true.
      * If false, and if supported by the frontend, any
      * on-screen fast-forward notifications will be
      * suppressed */
     bool notification;
  
     /* If true, the core will have sole control over
      * when fastforwarding mode is enabled/disabled;
      * the frontend will not be able to change the
      * state set by 'fastforward' until either
      * 'inhibit_toggle' is set to false, or the core
      * is unloaded */
     bool inhibit_toggle;
  };
  
  /* During normal operation. Rate will be equal to the core's internal FPS. */
  #define RETRO_THROTTLE_NONE              0
  
  /* While paused or stepping single frames. Rate will be 0. */
  #define RETRO_THROTTLE_FRAME_STEPPING    1
  
  /* During fast forwarding.
   * Rate will be 0 if not specifically limited to a maximum speed. */
  #define RETRO_THROTTLE_FAST_FORWARD      2
  
  /* During slow motion. Rate will be less than the core's internal FPS. */
  #define RETRO_THROTTLE_SLOW_MOTION       3
  
  /* While rewinding recorded save states. Rate can vary depending on the rewind
   * speed or be 0 if the frontend is not aiming for a specific rate. */
  #define RETRO_THROTTLE_REWINDING         4
  
  /* While vsync is active in the video driver and the target refresh rate is
   * lower than the core's internal FPS. Rate is the target refresh rate. */
  #define RETRO_THROTTLE_VSYNC             5
  
  /* When the frontend does not throttle in any way. Rate will be 0.
   * An example could be if no vsync or audio output is active. */
  #define RETRO_THROTTLE_UNBLOCKED         6
  
  struct retro_throttle_state
  {
     /* The current throttling mode. Should be one of the values above. */
     unsigned mode;
  
     /* How many times per second the frontend aims to call retro_run.
      * Depending on the mode, it can be 0 if there is no known fixed rate.
      * This won't be accurate if the total processing time of the core and
      * the frontend is longer than what is available for one frame. */
     float rate;
  };
  
  /* Callbacks */
  
  /* Environment callback. Gives implementations a way of performing
   * uncommon tasks. Extensible. */
  typedef bool (RETRO_CALLCONV *retro_environment_t)(unsigned cmd, void *data);
  
  /* Render a frame. Pixel format is 15-bit 0RGB1555 native endian
   * unless changed (see RETRO_ENVIRONMENT_SET_PIXEL_FORMAT).
   *
   * Width and height specify dimensions of buffer.
   * Pitch specifices length in bytes between two lines in buffer.
   *
   * For performance reasons, it is highly recommended to have a frame
   * that is packed in memory, i.e. pitch == width * byte_per_pixel.
   * Certain graphic APIs, such as OpenGL ES, do not like textures
   * that are not packed in memory.
   */
  typedef void (RETRO_CALLCONV *retro_video_refresh_t)(const void *data, unsigned width,
        unsigned height, size_t pitch);
  
  /* Renders a single audio frame. Should only be used if implementation
   * generates a single sample at a time.
   * Format is signed 16-bit native endian.
   */
  typedef void (RETRO_CALLCONV *retro_audio_sample_t)(int16_t left, int16_t right);
  
  /* Renders multiple audio frames in one go.
   *
   * One frame is defined as a sample of left and right channels, interleaved.
   * I.e. int16_t buf[4] = { l, r, l, r }; would be 2 frames.
   * Only one of the audio callbacks must ever be used.
   */
  typedef size_t (RETRO_CALLCONV *retro_audio_sample_batch_t)(const int16_t *data,
        size_t frames);
  
  /* Polls input. */
  typedef void (RETRO_CALLCONV *retro_input_poll_t)(void);
  
  /* Queries for input for player 'port'. device will be masked with
   * RETRO_DEVICE_MASK.
   *
   * Specialization of devices such as RETRO_DEVICE_JOYPAD_MULTITAP that
   * have been set with retro_set_controller_port_device()
   * will still use the higher level RETRO_DEVICE_JOYPAD to request input.
   */
  typedef int16_t (RETRO_CALLCONV *retro_input_state_t)(unsigned port, unsigned device,
        unsigned index, unsigned id);
  
  /* Sets callbacks. retro_set_environment() is guaranteed to be called
   * before retro_init().
   *
   * The rest of the set_* functions are guaranteed to have been called
   * before the first call to retro_run() is made. */
  RETRO_API void retro_set_environment(retro_environment_t);
  RETRO_API void retro_set_video_refresh(retro_video_refresh_t);
  RETRO_API void retro_set_audio_sample(retro_audio_sample_t);
  RETRO_API void retro_set_audio_sample_batch(retro_audio_sample_batch_t);
  RETRO_API void retro_set_input_poll(retro_input_poll_t);
  RETRO_API void retro_set_input_state(retro_input_state_t);
  
  /* Library global initialization/deinitialization. */
  RETRO_API void retro_init(void);
  RETRO_API void retro_deinit(void);
  
  /* Must return RETRO_API_VERSION. Used to validate ABI compatibility
   * when the API is revised. */
  RETRO_API unsigned retro_api_version(void);
  
  /* Gets statically known system info. Pointers provided in *info
   * must be statically allocated.
   * Can be called at any time, even before retro_init(). */
  RETRO_API void retro_get_system_info(struct retro_system_info *info);
  
  /* Gets information about system audio/video timings and geometry.
   * Can be called only after retro_load_game() has successfully completed.
   * NOTE: The implementation of this function might not initialize every
   * variable if needed.
   * E.g. geom.aspect_ratio might not be initialized if core doesn't
   * desire a particular aspect ratio. */
  RETRO_API void retro_get_system_av_info(struct retro_system_av_info *info);
  
  /* Sets device to be used for player 'port'.
   * By default, RETRO_DEVICE_JOYPAD is assumed to be plugged into all
   * available ports.
   * Setting a particular device type is not a guarantee that libretro cores
   * will only poll input based on that particular device type. It is only a
   * hint to the libretro core when a core cannot automatically detect the
   * appropriate input device type on its own. It is also relevant when a
   * core can change its behavior depending on device type.
   *
   * As part of the core's implementation of retro_set_controller_port_device,
   * the core should call RETRO_ENVIRONMENT_SET_INPUT_DESCRIPTORS to notify the
   * frontend if the descriptions for any controls have changed as a
   * result of changing the device type.
   */
  RETRO_API void retro_set_controller_port_device(unsigned port, unsigned device);
  
  /* Resets the current game. */
  RETRO_API void retro_reset(void);
  
  /* Runs the game for one video frame.
   * During retro_run(), input_poll callback must be called at least once.
   *
   * If a frame is not rendered for reasons where a game "dropped" a frame,
   * this still counts as a frame, and retro_run() should explicitly dupe
   * a frame if GET_CAN_DUPE returns true.
   * In this case, the video callback can take a NULL argument for data.
   */
  RETRO_API void retro_run(void);
  
  /* Returns the amount of data the implementation requires to serialize
   * internal state (save states).
   * Between calls to retro_load_game() and retro_unload_game(), the
   * returned size is never allowed to be larger than a previous returned
   * value, to ensure that the frontend can allocate a save state buffer once.
   */
  RETRO_API size_t retro_serialize_size(void);
  
  /* Serializes internal state. If failed, or size is lower than
   * retro_serialize_size(), it should return false, true otherwise. */
  RETRO_API bool retro_serialize(void *data, size_t size);
  RETRO_API bool retro_unserialize(const void *data, size_t size);
  
  RETRO_API void retro_cheat_reset(void);
  RETRO_API void retro_cheat_set(unsigned index, bool enabled, const char *code);
  
  /* Loads a game.
   * Return true to indicate successful loading and false to indicate load failure.
   */
  RETRO_API bool retro_load_game(const struct retro_game_info *game);
  
  /* Loads a "special" kind of game. Should not be used,
   * except in extreme cases. */
  RETRO_API bool retro_load_game_special(
    unsigned game_type,
    const struct retro_game_info *info, size_t num_info
  );
  
  /* Unloads the currently loaded game. Called before retro_deinit(void). */
  RETRO_API void retro_unload_game(void);
  
  /* Gets region of game. */
  RETRO_API unsigned retro_get_region(void);
  
  /* Gets region of memory. */
  RETRO_API void *retro_get_memory_data(unsigned id);
  RETRO_API size_t retro_get_memory_size(unsigned id);
  
  #ifdef __cplusplus
  }
  #endif
  
  #endif
  